"At the Zuyevka station in the Kirov region, the dead woman was urgently taken off the train. All the travellers, a group of migrants who were in her proximity, were also evacuated," the regional government said.

"Taking into account the unfortunate epidemiological situation in the People's Republic of China, all possible measures were taken to avoid the spread of an infection," the website statement said.

It did not give further details over its concerns about health issues in China.

According to officials in the remote region about 850 kilometres east of Moscow, the 53 people are being held at a hospital infections ward, and the results of their diagnosis will be known Thursday.

News agency RIA-Novosti initially quoted a local doctor as saying at least four of the passengers had elevated temperatures and the woman could have died of an "atypical pneumonia".

Some reports quoted local medical officials expressing concern the woman could have died of the highly contagious Severe Acute Respiratory Syndrome (SARS) that has killed hundreds in Asia, but the local health ministry said it was too early to tell.

"The reason for the sudden death of the girl has not yet been determined. She could have died of heart troubles or other illnesses," said Alla Oskina, deputy head of the ministry.

Regional governor Nikita Belykh vowed to "take all necessary measures" to protect the population in connection with unexplained death, the Interfax news agency reported.

Regional authorities identified the woman as a Chinese citizen born in 1985. The Chinese Embassy in Moscow said that it had not given permission for her autopsy, Interfax reported.

(c) 2009 AFP