The United States is removing some diplomatic staff from China because of fears over the outbreak of a deadly pneumonia.
China's health ministry says bug is under control
The World Health Organisation has told travellers to postpone non-essential trips to Hong Kong and China's Guangdong province - thought to be the epicentre of the outbreak.
There have been hundreds of probable cases of Severe Acute Respiratory Syndrome (SARS) and almost 80 deaths from the virus worldwide.
But the Chinese authorities insist the outbreak of the illness is under control and are urging people who had cancelled travel plans to reconsider.
"People live and work normally. The society is stable and travel safe," Health Minister Zhang Wenkang said on Thursday.
US Deputy Secretary of State Richard Armitage said all family members and non-essential diplomats would be offered free flights out of China.
The stakes are high, and the outcome cannot be predicted
The same offer has already been made to staff in Hong Kong.
The US decision came on the same day that Dr Julie Gerberding, a director of the US Centers for Disease Control (CDC), said that a massive scientific drive to beat the illness may be too late to prevent a major outbreak across every continent of the world.
WHO experts finally reached Guangdong province in China on Thursday where they will start work trying to unmask the source of the illness.
There have been 72 probable cases of Sars in the US so far, but Dr Gerberding fears that the worst could yet be to come.
In the New England Journal of Medicine, she wrote: "A very sobering question remains - are we fast enough?
Checking in at Bangkok airport
"Can we prevent a global pandemic of Sars?"
"If the virus moves faster than our scientific, communications and control capacities, we could be in for a long, difficult race.
"The stakes are high, and the outcome cannot be predicted."
The WHO said anyone intending to visit Hong Kong or Guangdong province "should consider postponing their travel until another time".
The view has been echoed by Professor Sir Liam Donaldson, England's chief medical officer, who said people travelling to these areas would be at "significant risk".
Three people so far have been admitted to hospital with suspected Sars cases.
Two have now been discharged - but one is still in hospital in London.
Sir Liam told the BBC: "It's clear that the disease hasn't come under control in Hong Kong and Guangdong province.
China 1190 cases (46 deaths)
Hong Kong 734 (17)
Vietnam 59 (4)
Canada 62 (6)
Thailand 7 (2)
"We're not looking at a global problem on the scale of the influenza epidemic which happened at the turn of the last century, but it is a pretty serious form of pneumonia."
Seventy nine people are now reported to have died worldwide.
Around 2,270 people have been infected worldwide, causing widespread fear and the imposition of emergency measures.
The WHO estimates Sars will prove fatal in around 4% of cases, usually where the person has an underlying condition such as diabetes or a weakened immune system.
But it said that in 90% of cases, people seem to recover around a week after being infected.
Scientists are worried about Sars because it is possible that it could, in some cases, become airborne and infect people far more easily.
If this is the case, then it would become far more difficult to contain.
There is now strong evidence that the illness is caused by a new strain of Corona virus, although this is not yet proven.
The WHO delegation in Guangdong province will investigate theories that the virus "jumped" from animals into humans.
The WHO travel advice does not apply yet to other areas, such as Singapore, Vietnam or Canada, where outbreaks appear to have been effectively contained.
As well as the latest deaths in Guangdong, China said there were 361 new cases in the province in March.
Health officials said several cases of Sars have also been discovered in Shanghai, China's second-largest city.
In Taiwan, a 30-minute public information programme about the risks of Sars was broadcast on Thursday.
Teachers, government employees and servicemen were all "obliged" to watch it.
Meanwhile, Canada, the worst-affected country outside Asia, said two more people have died from Sars in Toronto, bring to six the total number of fatalities in Canada.
The country has imposed mandatory quarantine on two people it said had been in contact with Sars patients, and were choosing to disregard instructions to stay away from other members of the public.
In Thailand, authorities have said that they are prepared to quarantine - for weeks if necessary - every passenger on any aircraft found to be carrying a Sars patient.