Hong Kong has decided to impose a mandatory 14-day quarantine on all visitors from mainland China as it battles to prevent the spread of a coronavirus outbreak.

The policy comes into effect on February 8, but officials refused to close the border entirely, as demanded by medical staff who have gone on strike.

Hong Kong, which has 21 confirmed cases and one fatality, suffered 300 deaths in the SARS outbreak in 2002-2003.

There are 24,300 confirmed coronavirus cases and 490 deaths in mainland China.

Those figures included an additional 4,000 cases and 65 deaths on February 4.

The new virus has spread overseas, with 25 nations confirming a total of 191 cases, although there has so far been only one death, in the Philippines.

The WHO has declared the outbreak a global health emergency. On February 5, WHO chief, Tedros Adhanom Ghebreyesus appealed for $675 million to fund a three-month response plan.

Meanwhile, at least 10 people on board a cruise ship docked in the Japanese port of Yokohama have tested positive for the virus.

The coronavirus causes severe acute respiratory infection and symptoms usually start with a fever, followed by a dry cough. Most people infected are likely to fully recover – just as they would from a flu.

Hong Kong Chief Executive Carrie Lam said anyone arriving from the mainland, including foreigners, would be quarantined for 14 days from February 8, although she did not say how this would be imposed.

It is unclear where the quarantines would take place or whether Hong Kong residents could spend the time at home.

Tens of thousands of people arrived from the mainland on February 4.

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Carrie Lam has not moved to close the border entirely, although thousands of medical staff on February 5 entered the third day of their strike over the issue and have threatened to escalate their action.

Hong Kong will, however, close the Ocean and Kai Tak cruise terminals.

Some 3,600 passengers and crew on the World Dream, docked at Kai Tak, are being tested for the virus after three Chinese passengers who were on the ship between January 19 and 24 tested positive after disembarking.

Hong Kong remains concerned about a repeat of the deadly Severe Acute Respiratory Syndrome (SARS) outbreak, although the mortality rate of the new virus is much lower than that of SARS, which was around 9.6%.

There have been massive queues for masks which are in short supply and are selling at inflated prices.

Separately, the Hong Kong-based airline Cathay Pacific is asking 27,000 staff to take three weeks unpaid leave over the coming months as it deals with the impact of the outbreak.