Nevertheless, restrictions were tightened in Hubei yesterday with a ban on vehicles, apart from essential services, and companies told to stay shut until further notice.

Outside mainland China, there have been about 500 cases in some two dozen countries and territories, with 5 deaths - in Japan, Chinese-ruled Hong Kong, the Philippines, France and Taiwan.

The biggest cluster outside China has been on the Diamond Princess cruise ship quarantined off Japan's Yokohama, with 70 more cases reported yesterday, taking the total to 355 of the roughly 3,700 passengers and crew on board.

Those testing positive are sent to hospital. No one from the ship has died of the virus.

The US Embassy in Tokyo said passengers and crew were at high risk of exposure to the virus and it recommended that the estimated 400 US citizens onboard get off and take one of the evacuation flights it is arranging yesterday.

"This is a rapidly evolving situation," the embassy said in a notice.

The embassy said everyone would be screened before being allowed to board the chartered flights and quarantined for 14 days upon arrival back in the United States.

"No symptomatic or infected passengers will be allowed to board," it said.

Hong Kong, Canada, Italy and South Korea also said they planned to evacuate their citizens from the ship.

Another cruise ship, Holland America's MS Westerdam, docked in Cambodia on Thursday after being rejected by ports in several other countries and territories.