A major cruise line has taken the extraordinary step of banning citizens of China, regardless of when they were last there.

Royal Caribbean Cruises Ltd issued a statement on Friday saying: "Any guest or crewmen travelling from, to, or through mainland China, Hong Kong or Macau less than 15 days prior to their sailing will be unable to board any of our ships."

It also said, "Any guests holding a Chinese, Hong Kong or Macau passport, regardless of when they were there last, will not be allowed to board our ships."

It comes amid growing concerns over spreading coronavirus, which has killed more than 700 people and affected people in at least 25 different countries.

China has complained bitterly about bans and measures that go against World Health Organisation recommendations and accused governments and companies that take such actions of fear-mongering.

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Two deaths have been reported outside mainland China, in Hong Kong and the Philippines, but how deadly and contagious the virus remains unclear, prompting countries to quarantine hundreds of people and cut travel links with China.

Four sick passengers aboard a Royal Caribbean ship that arrived off New Jersey in the United States were sent to a hospital out of "an abundance of caution," the local mayor said.

There were 41 new cases among about 3,700 people quarantined in a cruise ship off Japan, taking the total to 61, while Chinese-ruled Hong Kong quarantined for a third day a cruise ship with 3,600 on board.

"A cruise ship is a very particular environment in which you can have higher levels of transmission even with a virus that isn't very efficient at transmission," WHO emergency expert Mike Ryan told a news conference in Geneva.

The head of the Beijing Municipal Bureau of Justice, Li Fuying, told reporters that people deliberately concealing contacts or refusing isolation could be punished with death.