Britain was on alert today as a deadly outbreak of swine flu which has claimed 81 lives in Mexico spread around the world.
Nearly 1,300 people are thought to be infected around the world as doctors in France, Spain, New Zealand and Israel are already treating people who may have contracted the illness.
There have also been confirmed outbreaks in America as the World Health Organisation warned of the possibility of a global pandemic.
Members are due to meet on Tuesday to decide if the alert level should be raised.
Today churches in heavily Catholic Mexico City stood empty after services were cancelled in the wake of the outbreak.
Hundreds of public events from concerts to sports matches throughout the country were called off to keep people from congregating and spreading the virus in large crowds.
Today, New York health officials said more than 100 students at the St. Francis Preparatory School, in Queens, recently began suffering a fever, sore throat and aches and pains. Some of their relatives also have been ill.
Some of the St. Francis students had recently travelled to Mexico, The New York Times and New York Post reported today.
Preliminary tests of samples taken from sick students' noses and throats confirmed that at least eight had a non-human strain of influenza type A, indicating probable cases of swine flu, city health officials said.
The exact subtypes were still unknown, and the federal Centers for Disease Control and Prevention was conducting further tests.
Suspected cases have also been found in several other countries around the world.
Mexican soldiers and health workers have been patrolling airports and bus stations in search of those showing symptoms, which include a fever of more than 100 F, body aches, coughing, sore throat, respiratory congestion and in some cases, vomiting and diahorrea.
New Zealand's health minister says 10 students who were recently in Mexico have tested positive for influenza. He said the cases are 'likely' to be swine flu.
Tony Ryall has said that 13 high school students who returned from Mexico yesterday were tested for swine influenza, and 10 had positive results. The results have been sent to the World Health Organization lab in Melbourne, Australia.
Mr Ryall said there was 'no guarantee' the students had swine flu, but that health officials were taking precautions. He added today that none of the patients were seriously ill and seemed to be recovering.
The UK was also on alert last night after a British Airways cabin crew member complained of 'flu-like symptoms' midway through a flight to Heathrow from Mexico City, where the virus first surfaced.
The unnamed man, understood to be a British national, was put in isolation in a West London hospital and was being treated by staff trained in infectious disease controls.
But this morning it emerged that the patient did not in fact have the illness.
A spokesman for Northwick Park Hospital said: 'I can confirm he does not have swine flu. All the tests have come back negative.'
The Spanish government today confirmed that it was also investigating three suspected cases of swine flu.
A Health Ministry spokesman said cases were being investigated in Valencia, Bilbao and Albacete, inland from Alicante in south-east Spain. The official stressed that none of the cases had been confirmed. It was not immediately known if any of the patients had recently visited Mexico.
French Health Ministry officials said four possible cases of swine flu are currently under investigation, including a family of three in the northern Nord region and a woman in the Paris region. The four recently returned from Mexico. Tests on two separate cases of suspected swine flu proved negative, they said.
Israel said a man who had recently visited Mexico had been hospitalized while authorities try to determine whether he had the disease.
Earlier, panic spread throughout Mexico, where those who died were reported to be the first victims of a pandemic with the potential to kill millions.
The new flu strain, a mixture of various swine, bird and human viruses, poses the biggest risk of a large-scale pandemic since avian flu surfaced in 1997, killing several hundred people, and a 1968 'Hong Kong' flu pandemic killed about 1 million people globally.
New flu strains can spread quickly because no one has natural immunity to them and a vaccine takes months to develop.
Countries across Asia, which have had to grapple with deadly viruses like H5N1 bird flu and SARS in recent years, have snapped into action. Airports and border checkpoints in Hong Kong, Malaysia, South Korea and Japan have been screening travellers for any flu-like symptoms.
In Egypt, health authorities were examining about 350,000 pigs being raised in Cairo and other provinces for swine flu.
Argentina has declared a health alert, requiring anyone arriving on flights from Mexico to advise if they had flu-like symptoms.
Russia imposed curbs on meat imports from Mexico, some U.S. states and the Caribbean, while the United Arab Emirates said it was considering similar action.
As well as the 81 dead – mostly aged between 25 and 45 – more than 1,300 patients were being treated in Mexico for respiratory infections that showed signs of the new strain.
The same virus type has appeared in Texas, California, Kansas and New York. A total of 19 people have been infected, eight of whom have recovered.
Last night it was reported that President Barack Obama had met one of the possible victims earlier this month.
He was greeted on his visit to Mexico City on April 16 by archaeologist Felipe Solis, who died the following day from flu-like symptoms.
A White House spokesman confirmed yesterday that Mr Obama's health was fine. 'The president's trip to Mexico has not put his health in any danger,' he said.
Barack Obama: The President's trip to Mexico did not put his health in danger
The President was in Mexico last week to meet with top government officials and talk about the growing problem of drug smuggling and border violence.
Mexico's health secretary, Jose Cordova, said Mr Solis had a pre-existing illness and died of pneumonia unrelated to influenza.
Tests on Saturday night also showed that eight students who fell ill at a school in New York with flu-like symptoms on Thursday and Friday also had the virus.
A US government source said ‘hundreds’ of Americans had been in contact with infected people and that it was now urgent that this group be tested.
There is no vaccine for the new strain, but patients who become ill with it can be treated with anti-viral drugs.
It is expected that all travel to and from Mexico will be halted and that any Britons in California, New York and Kansas will be instructed to get full medical check-ups before flying back to Europe.
Mexico’s health secretary, Jose Angel Cordova, went on national television yesterday to issue a stark warning. He said: ‘This is highly contagious. It can be fatal and it has pandemic properties.
Neighbouring California has made a 'rigorous and thorough' response to the new strain, Governor Arnold Schwarzenegger said.
The BA attendant was taken from BA flight 242 to Northwick Park Hospital in Harrow and was said to be responding well to treatment.
Medics from the Heathrow Port Health Authority were waiting at the airport when the aircraft landed. They boarded the jumbo jet and kept passengers waiting on board while they examined the steward.
Danger: Women wear surgical masks as they exit the subway
Yesterday afternoon, BA provided 30 face masks for crew on the next flight to Mexico from Heathrow. Sources said they had bought all the masks on sale at Boots in the airport.
A cabin crew source said: ‘BA bought 30 masks from Boots because there are concerns about the spread of this flu in Mexico. There is no Mexico flight from Heathrow on Sunday, and we are hoping that by the time Monday’s flight leaves London, BA will be able to find more masks so that our crew can be protected if needs be. The same happened a while ago during the SARS outbreak.’
A Northwick Park Hospital spokesman said: ‘The patient was admitted directly to a side room and the hospital is scrupulously following infection control procedures to ensure there is no risk to any other individual in the hospital.’
Mexico City canceled hundreds of public concerts, sporting events and meetings on Saturday as authorities tried to contain the outbreak
The Health Protection Agency said: ‘We are aware of a patient admitted to a London hospital with reported travel history to Mexico. As a precautionary measure the patient is being tested for a range of respiratory and other illnesses in line with UK health guidance. At present there have been no confirmed cases of human swine flu anywhere in Europe.’
World Health Organisation director-general Margaret Chan said the outbreak in Mexico involves ‘an animal strain of the H1N1 virus’.
Those who died in Mexico – where the first case was confirmed on April 13 – had not been in contact with animals. Mr Cordova said: ‘This probably started with pigs but has now mutated to pass between humans.’
An organ grinder, wearing surgical masks as a precaution against infection
The age of the victims last night heightened fears that the virus could be the beginning of a pandemic – most victims of the so-called Spanish flu that wiped out about 50million people after the First World War were men and women in their prime.
Medical experts said last night that while starting like a normal flu, victims’ temperatures soon shot to 102F, with muscle aches so painful they were almost paralysing. The flu is also characterised by extremely painful headaches and eventually diarrhoea and vomiting.
The Mexican government began a mass immunisation programme, but abandoned it on Friday after it was acknowledged that the vaccines offered no protection against the new killer virus.
A police officer, wearing a surgical mask as a precaution against infection, directs traffic in downtown Mexico City
In efforts to stop the disease spreading, the authorities ordered all schools and universities across Mexico City to close until further notice.
‘The worst thing is that you don’t know who has this virus,’ said Gisela Hernandez, a 34-year-old housewife. ‘Maybe your neighbour has got it. Maybe the guy in the corner shop or the restaurant has it.’
California Governor Arnold Schwarzenegger, pictured at NASA's Ames Research Center yesterday, said the state is coordinating with federal and international health experts on its plan to fight the flu
It is thought people can carry the virus for up to seven days before symptoms show. Michael Osterholm, a pandemic flu expert at the University of Minnesota, said new cases were probably already incubating across he world.
Tamiflu, an antiviral drug used against bird flu, is said to be effective against the new strain.
Swine flu is a respiratory disease, normally confined to pigs. Only a few human cases have been reported in the past, mostly among farm workers, however, flu viruses can mutate into deadly new forms.
The WHO's pandemic alert level is currently at to phase 3. The organization said the level could be raised to phase 4 if the virus shows sustained ability to pass from human to human.
Phase 5 would be reached if the virus is found in at least two countries in the same region.
'The declaration of phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short,' WHO said.
Phase 6 would indicate a full-scale global pandemic.
He advised people to stay in their homes if possible, keep away from public places and avoid physical contact.