By Tay Han Nee

HONG KONG (Reuters) - A tanker with about half of its 24-member crew showing symptoms of SARS made a distress stop in Hong Kong Sunday in what could be the first large outbreak of the disease in a vessel at sea.

China, the country worst hit by the Severe Acute Respiratory Syndrome, ordered schools in Beijing to remain closed for another two weeks to contain the spread of the disease while Singapore charged a 50-year-old man who violated quarantine after being exposed to the virus.

The city-state has enforced some of the strictest measures in the world to prevent the spread of SARS and has repeatedly said it will prosecute anyone who does not obey quarantine orders. But it was the first time a violator had been detained.

At least 436 people have been killed by SARS, most of them in mainland China and in Hong Kong. About 6,500 have been infected.

In Hong Kong, doctors and paramedics clad in white protective suits boarded the "Bunga Melawis Satu" shortly after the Malaysian-flagged vessel dropped anchor off the territory. Rescue helicopters flew overhead to take victims to hospital if needed.

The captain of the vessel, which is carrying chemicals and was originally bound for the southern Chinese port of Guangzhou, made the emergency appeal to dock in Hong Kong after 10 crew members were found to be ill with fever, coughs and bodyaches, symptoms of SARS. One is seriously sick.

There is no standard treatment for SARS, which is mainly passed by droplets through sneezing and coughing.

"Three doctors have gone up to the tanker and are checking to see if the 10 crew may have SARS. We have a hospital on standby," said a Health Department spokeswoman.

"We don't know if any of them will be taken to hospital. The doctors are still checking to see if they have SARS."

A port source in Hong Kong said the vessel had been in Singapore and Malaysia before it docked in Thailand. It left Thailand on April 28.

"It was going about its normal business while traveling from Singapore to Malaysia and to Thailand," said the port source.

"The crew appear to have fallen ill while at sea after leaving Thailand," he added.

CREW OF INDIAN ORIGIN

It is not known how or where the sick crew members, all of Indian origin, contracted their illnesses. The SARS virus usually takes between two and seven days to incubate before a victim begins showing symptoms.

Beijing, with a population of 14 million, is the worst-hit city in the world. Almost 100 people have died of SARS there, about 1,750 have been infected and the number of cases rises by about 100 each day.

Authorities said elementary and primary schools in the city would remain closed for another two weeks because of SARS. They were due to open on Monday after a two-week suspension.

Concern is also growing about the spread of the disease to the impoverished countryside, home to more than 70 percent of China's 1.3 billion people but where hospitals receive only 20 percent of national funding.

On Saturday, the government tripled funds set aside to fight SARS to $725 million and said the money would be used to buy medical equipment in the hinterland and to pay for the bills of impoverished rural and urban patients.

On Saturday, Hong Kong reported only 10 fresh SARS infections, the lowest daily total for a month and a half. But authorities warned the disease was not yet under control and that more people were likely to die.

Hong Kong has reported about 1,600 SARS cases of whom about 900 are still being treated. Of these, about 80 are in serious condition. A total of 179 people have died of SARS so far in the territory.

Singapore, which has seen 25 deaths due to SARS, has quarantined 3,154 people and threatened them with fines of $5,649 or six months in jail if they leave their homes.

Newspapers reported on Sunday that police detained a 50-year old Chinese man who broke his home quarantine order.

The Ministry of Health said the man was being held at a special isolation facility for the remaining period of his quarantine and that his case was being investigated.