The new case, a 49-year-old retired female doctor, shared a Beijing hospital room with one of the two people already confirmed to have the respiratory disease, the health ministry said.

It brings to seven the number of suspected Severe Acute Respiratory Syndrome patients in Beijing and eastern Anhui province.

All the cases are linked to the Institute of Virology in the Chinese capital, believed to be the source of the outbreak.

In a wake-up call to neighbouring countries, the ministry said 18 nationals from Australia, Japan, South Korea and Russia had visited the laboratory since March 1.

It gave no details on whether they had since returned home but "the ministry has informed the visitors' countries concerned and the World Health Organization of relevant information and no abnormal problems have been reported yet".

A researcher at the institute contracted SARS and infected a nurse who took care of her at a Beijing hospital earlier this month. The nurse in turn infected the female doctor.

The researcher's mother has since died, while the nurse's relatives and other contacts have also gone down with symptoms of the disease.

The ministry said one more person under observation had a fever, but had yet to be classified as having SARS symptoms.

Since the first case was reported on April 22, 700 people have been put under medical observation in Beijing, said Wu Jiang, director of the infectious disease control department of the Beijing Centre of Disease Control.

"Since the latest SARS outbreak 700 people have been put under medical observation, but don't forget that some have already been released," he told

"For us every day the figure is changing. People are being released and people are being put in isolation."

Xinhua said Wednesday 143 people in Anhui have been confirmed as having close contact with the SARS patient there. So far, 36 have been released from hospital while 78 remain in isolation. None of them show SARS symptoms.

It failed to say what happened to the remaining 29.

China's mounting problems came as World Health Organisation experts converged on Beijing to access the situation, and Chinese authorities called on people to "trust" the government.

"So far, the epidemic investigation for SARS in Beijing was quick, accurate and efficiently saved time for the whole campaign to prevent and control the disease ...," said Beijing Health Bureau deputy director Liang Wannian

Liang was quoted by Xinhua as urging people to "trust the government's capacity to control SARS" amid concern that the disease could spread with millions on the move during Labour Day holidays starting Saturday.

In Beijing, the WHO said teams of experts would fan out around the country, paying special attention to bio-safety standards.

"Members of the group ... have expertise in epidemiology, virology, infection control, and laboratory bio-safety," said WHO spokesman Bob Dietz.

"Some members will travel to Anhui province to work there. Others will work closely with Beijing health authorities.

"A prime task of the WHO experts and their Chinese counterparts will be to conclusively decide if the laboratory was indeed the source of these people's infections," said Dietz.

Last year SARS killed nearly 800 people and infected more than 8,000 worldwide, with Beijing the worst-hit city in the world.

The Chinese government initially covered-up the outbreak, with the health minister and Beijing mayor paying for it with their jobs.

TERRA.WIRE