The UK government is failing to do enough to protect people against the rising threat of Sars, say the Conservatives.
Fear of the disease is spreading
Opposition leader Iain Duncan Smith has called for new powers to be brought in so that anyone showing symptoms of the disease can be put in quarantine.
However, England's Chief Medical Officer Sir Liam Donaldson told the BBC that the UK was already taking sufficient precautions against the disease.
He said there was no need to make Sars a "notifiable disease", which would allow suspected cases to be forcibly quarantined.
Concern has been raised over the thousands of travellers from Sars-hit regions arriving in the UK every week.
We have been very very precautionary in our handling of this outbreak
Professor Sir Liam Donaldson, Chief Medical Officer, England
The World Health Organisation (WHO)has warned against visiting Hong Kong, Beijing and Toronto as the number of cases there spiral.
So far, well over 250 people have died from the pneumonia caused by the infection, and more than 4,000 cases have been reported to the WHO worldwide.
However, in the UK, there have so far been only six cases, and no deaths.
An estimated 16,000 people are carried into Britain every week on flights from these cities - and there are worries that screening of incoming passengers is inadequate.
Two British experts said on Thursday that they felt Sars was potentially more dangerous than HIV - as it was much easier to catch.
Professor Peter Openshaw, from Imperial College London, told the BBC: "It's difficult to know how bad it's going to be.
"It's got a lot of ingredients that make it more threatening and worrying than HIV."
Dr Patrick Dixon, who predicts global trends, said that millions would be affected if the disease continued to spread at the same rate.
He said if the disease became established in developing countries, the death toll would be much higher.
He told the BBC: "This is not something that should be handled by bureaucrats at the Department of Health - it should be dealt with at number 10 Downing Street."
It's got a lot of ingredients that make it more threatening and worrying than HIV
Professor Peter Openshaw, Imperial College
The UK has one of the most advanced health surveillance systems in the world - and, unlike Toronto, has had advanced warning of the threat of Sars.
The Department of Health backed the WHO travel advice - it is also urging people to stay away from Toronto, Hong Kong and Beijing.
Sir Liam told the BBC: "We have been very very precautionary in our handling of this outbreak.
"We have had six cases - they have been detected quickly and brought under control."
"We remain very concerned about the situation worldwide."
The government's response has been feeble
Dr Liam Fox, Shadow Health Secretary
However, Shadow Health Secretary Dr Liam Fox accused ministers of failing to take the right steps to protect the public.
He said: "We need to take all powers under the legislation to make sure the public are properly protected - we're not dong that at the moment.
"The government's response has been feeble and ministers virtually invisible."
Passengers returning from the far East have told the BBC that few steps appeared to taken at airports to spot people showing symptoms of Sars.
One said: "With the exception of being asked if I have any symptoms, there was no screening - I just walked through."
Corona virus - may cause Sars
Some airports in the far East have been taking the temperature of all incoming passengers to spot those who might have a fever.
Current UK advice suggests that people who have been to Sars-affected areas who develop a high temperature, dry cough and difficulty breathing should contact their doctor immediately.
Doctors' leaders warned against an over-reaction to the Sars threat.
Dr Vivienne Nathanson from the British Medical Association said: "There is no reason to close the UK's borders.
"This is not practical as it would have to extend to all countries which have had cases, including the USA.
"Such a move would also stop all commerce, imports and exports like food and this would be a gross over-reaction to the threat."