Ten people on a cruise ship anchored off Japan have tested positive for the novel coronavirus.

The Diamond Princess is anchored off Yokohama, and all 3700 passengers and crew have been quarantined.

Japanese health officials have tested dozens of people, and of 31 people whose test results have come through, 10 were confirmed as infected. All the infected have been hospitalised.

As of Tuesday, the outbreak has infected over 20,000 people and killed more than 400, most of them in China.

Common Wuhan coronavirus symptoms include fever, cough, shortness of breath and breathing difficulties.

Experts are unsure of whether the virus is able to transmit before symptoms appear or after.

If it worsens it can cause pneumonia, severe acute respiratory syndrome, kidney failure or even death.

The virus can be spread from animals to people.

But it also can be spread by coughing, sneezing and through close contact with an infected person or an object carrying the virus.

Experts are still figuring out how long an infected person is contagious as they try to determine a point of transmission.