A top Chinese official has said the mystery virus which has claimed more than 100 lives worldwide is not under control in China.
Dr Zhong: "How can you control it if its origin is unclear"
Zhong Nanshan, director of the Guangzhou Institute of Respiratory Diseases in Guangdong province - where the Severe Acute Respiratory Syndrome (Sars) is believed to have emerged - said it was better to describe the illness as "contained".
China has repeatedly made assurances that the bug is under control.
The World Health Organization (WHO) announced on Friday that it is to beef up its team of investigators in China to try to gain a better understanding of the disease, and develop better strategies to prevent its spread.
So far, the illness has infected at least 2,700 people worldwide, and killed at least 106, according to the WHO.
Common cold link
Studies now strongly suggest that a new strain of Corona virus, which normally causes the common cold, could be to blame.
According to an infectious disease expert, the mystery illness is probably in Asia to stay.
Dr Jim Hughes, from the US Centers for Disease Control, said that he believed that Sars - could not now be eradicated in the Far East.
SARS: PROBABLE CASES AND DEATHS
China 1,290 cases (55 deaths)
Hong Kong 970 (27)
Singapore 126 (9)
Vietnam 62 (4)
Canada 97 (10)
Thailand 7 (2)
Malaysia 3 (2)
Source: WHO (0600 GMT Friday)
Note: The WHO only records cases and deaths it believes are "probable" Sars - figures from national health authorities may vary.
Dr Hughes, the head of infectious diseases at the CDC, said that it was also possible that the illness would become a perennial feature of life in North America.
"In terms of its introduction into North America, whether it is here to stay I think remains to be seen but I think we should assume that it may well be."
His warning comes a week after a colleague, CDC director Dr Julie Gerberding, said that intensive efforts to contain Sars might fail.
The United States Government is recommending that Americans defer non-essential travel to China.
In Guangdong, 24 new cases were reported between Wednesday and Thursday, bringing the province's total to 1,237.
In Shanghai, a health official and the US Consulate said two Americans and five other foreigners were hospitalised
with possible cases of SARS.
The WHO has launched a review of health facilities in Beijing as part of efforts to bring the disease under control.
Official figures show a total of 22 people have been infected in Beijing - four of them have died. However, reports suggest that the true numbers could be higher.
Chinese state media reports that nationals from Finland, Canada, Hong Kong, Macau and Taiwan have come down with Sars.
A Finnish official with the International Labour Organisation, Pekka Aro, died of the virus.
On Thursday, friends of a US citizen who died from Sars claimed he had been wheeled, already dead, into an ambulance and sent from Beijing to Hong Kong because China's authorities did not want to report that another foreigner had died of the virus in the city.
The Canadian embassy said one of its nationals is infected but is recovering.
Hong Kong reported four more deaths on Thursday, pushing its total past 30 - although the WHO has yet to include these in its latest statistics.
In other developments:
Malaysia continued to block entry of visitors from China and Hong Kong, despite protests from tour operators who feared it would batter the tourism industry.
Philippines President Gloria Arroyo asked overseas compatriots who suspect they may have been infected with Sars to stay away, ahead of the Easter holidays. The Philippines reported its first "probable" case of the virus on Friday. However, officials said the 64-year-old male foreigner has since been cured.
Two crew members of a luxury cruise ship, with more than 800 passengers on board, have been confined at a Singapore hospital, with suspected Sars.
An unidentified British man is being treated in hospital in Jakarta, as Indonesia's first probable case of Sars.