Eleven of the 16 sailors from a Panamanian vessel who tested positive for novel coronavirus have been hospitalized for treatment in Zhoushan, Zhejiang province, as of Monday night, according to a senior official in the city.

The 11 sailors are in stable condition in wards of a local hospital designated to treat COVID-19 patients, said Fang Wei, vice-mayor of Zhoushan, at a news conference on Tuesday.

The remaining five infected sailors, who have mild symptoms, had to be treated onboard the vessel, the Grand Progress, because the ship needs the rest of the crew to be on duty, Fang said.

"But those patients remaining onboard will also be sent ashore for treatment when the crew management company's new crew arrives," she said.

The Zhoushan city government has set up a special task force to handle the matter and has initiated emergency procedures.

Nine sailors aboard the Grand Progress sought medical help in Zhoushan when they developed fevers on Aug 3.

The owner of the vessel contacted city departments to seek help on Friday.

The vessel, which has a total of 20 Chinese sailors, left the Philippines on July 30. Before that, it was docked in Indonesia from July 2 to 14.

The Grand Progress is now berthed at its designated anchorage site in Zhoushan waters. Health authorities collected swab samples and blood from the entire crew of 20 for nucleic acid testing and other tests on Monday. Sixteen of them tested positive for the coronavirus.

A first group of medical workers, including six doctors, have boarded the vessel to help treat the patients and disinfect the vessel to prevent further spread of the virus, Fang said.

Zhoushan is a port for many international ocean routes. The city usually has more than 7,000 sailors from around the world and 300 foreign vessels berthed in its harbor and at its piers each day.

Xu Fangming, deputy director of the Zhoushan health commission, said city departments will strictly follow the requirements of COVID-19 prevention and control regulations and form plans to ensure the safety of the sailors.

A similar situation has been reported in Ningde, Fujian province. A sailor on an arriving vessel also tested positive for coronavirus on Monday, the city health commission reported in a statement on Tuesday.

Ningde has established a special task force to handle the case and required the rest of the crew to stay onboard for medical observation, the statement said

Nucleic acid tests of the other sailors have been negative so far, it said.