About 3700 people are in a two-week quarantine on a cruise ship off Yokohama, Japan, after 10 passengers tested positive for coronavirus, health authorities say.

Photo: Kazuhiro NOGI / AFP

on board a cruise ship docked in the Japanese port of Yokohama have tested positive for coronavirus, health authorities say.

At least 10 people of the almost 300 passengers tested so far on the Diamond Princess have tested positive. The ship was carrying about 3700 people and the number of infected could rise as testing continues.

The checks began after an 80-year-old Hong Kong man who had been on the ship last month fell ill with the virus.

All 10 confirmed cases were in those over the age of 50, Japanese broadcaster NHK said.

Four were in their 50s, four in their 60s, one in their 70s, and another in their 80s. None were in "serious condition", NHK said.

Japanese Health Minister Katsunobu Kato said the confirmed cases were among 31 results from 273 people tested so far.

"We had them [the ones who tested positive] get off the vessel and ... we are sending them to medical organisations," he said at a news conference on Wednesday.

In China alone, there are now more than 24,300 cases of the virus, with the death toll at 490.

There is a much smaller number of cases in other countries around the globe - two people outside of mainland China have died of the disease.

The Hong Kong man believed to have been the source on the ship boarded in Yokohama, Japan, on 20 January and disembarked in Hong Kong on 25 January. He was only later found to have tested positive for the virus.

Officials on the cruise ship began screening guests on Monday evening, and the vessel was placed under quarantine on Tuesday.

What happens to the passengers now?

Passengers and crew on the ship will now be under quarantine for 14 days. The incubation period of the virus is believed to be about two weeks.

"We are now officially in quarantine. We are to remain on board the ship and we are confined to our cabins," a British passenger identified as Mr Abel told the Press Association news agency.

Another passenger said her mother, in her 80s, was running out of medicine.

"We are in trouble because [her] medicine is running out. Many of the passengers are old and some are as troubled as we are," she told NHK.

The Diamond Princess cruise ship is part of the Princess Cruises line owned by British-American cruise operator Carnival Corporation.

There are now 20 confirmed coronavirus cases in Japan, excluding the cruise ship infections.

Separately on Wednesday, 1800 passengers onboard a cruise ship docked in Hong Kong were also being tested for the virus.

Local media reports said three Chinese passengers who had spent time on the ship tested positive for the virus after disembarking.

The infected passengers were on the ship between 19 and 24 January. Hong Kong health officials said none of those on board had contact with the three passengers.

Some 30 crew members of the cruise liner said they were suffering symptoms of the virus and were also being tested.

Last week, more than 6000 people onboard a cruise ship in an Italian port were put on lockdown over fears that a Chinese passenger could be carrying the virus.

The passenger later tested negative for the novel coronavirus.

- BBC