China faced deepening isolation over its coronavirus epidemic on Saturday as the death toll soared to 259, with the United States and Australia leading a growing list of nations to impose extraordinary Chinese travel bans.

With Britain, Russia and Sweden among the countries confirming their first infections, the virus has now spread to more than two dozen nations, sending governments scurrying to limit their exposure.

China toughened its own quarantine measures at the centre of the outbreak in Hubei province, a day after the United States temporarily barred entry to foreigners who had been in China within the past two weeks.

"Foreign nationals, other than immediate family of US citizens and permanent residents... will be denied entry into the United States," Health Secretary Alex Azar said.

Australia said it was barring entry to non-citizens arriving from China, while Australian citizens who had travelled there would be required to go into "self-isolation" for two weeks.

Vietnam suspended all flights from mainland China effective Saturday. Hong Kong, Macau and Taiwan also initially appeared on the list of banned routes but were later removed.

Similar expansive restrictions have been announced by countries including Italy, Singapore, and China's northern neighbour Mongolia.

The United States, Japan, Britain, Germany and other nations had already advised their citizens not to travel to China.

Britain said Saturday it was temporarily withdrawing some diplomatic staff and their families from across the country, a day after the US State Department ordered embassy employees to send home family members under the age of 21.

Beijing insists it can contain the virus and called Washington's advice against travel to China "unkind".

"Certainly it is not a gesture of goodwill," foreign ministry spokeswoman Hua Chunying said.

The US emergency declaration also requires Americans returning from Hubei province to be placed in mandatory 14-day quarantine, and health screening for American citizens coming from other parts of China.

The virus emerged in early December and has been traced to a market in Hubei's capital Wuhan that sold wild animals.

It spread globally on the wings of a Lunar New Year holiday rush that sees hundreds of millions of Chinese people travel domestically and overseas.

The economic fallout continued Saturday as Apple announced that all its China stores would be closed until February 9.

China's central bank said it would offer financial support to businesses hit by the public health emergency.

With public anger mounting in China, Wuhan's top official admitted late Friday that authorities there had acted too slowly.

"If strict control measures had been taken earlier the result would have been better than now," said Ma Guoqiang, the Communist Party chief for Wuhan.

Wuhan officials have been criticised online for withholding information about the outbreak until late December despite knowing of it weeks earlier.

China finally lurched into action last week, effectively quarantining whole cities in Hubei and tens of millions of people.

Unprecedented safeguards imposed nationwide include postponing the return to school, cutting bus and train routes, and tightening health screening on travellers nationwide.

On Saturday, authorities in Hubei extended the new year holiday until February 13 and announced a suspension of marriage registrations from Monday to discourage public gatherings.

The city of Huanggang, east of Wuhan, said only one member of each household would be permitted to leave the house every two days to buy necessities. But the toll keeps mounting at an ever-increasing pace, with health authorities on Saturday saying 46 more people had died in the preceding 24 hours, all but one in Hubei.

Another 2,102 new infections were also confirmed, bringing the total to nearly 12,000 - far higher than the Severe Acute Respiratory Syndrome outbreak of 2002-03.

SARS, which is caused by a pathogen similar to the new coronavirus and also originated in China, killed 774 people worldwide - most of them in mainland China and Hong Kong.

The World Health Organization declared the outbreak a global emergency on Thursday but later warned that closing borders was probably ineffective in halting transmission and could accelerate the virus's spread.

But authorities around the world pressed ahead with preventive measures.