BEIJING - A new coronavirus has killed 25 people in China and infected more than 800, the government said on Friday, as the World Health Organisation declared it an emergency but stopped short of declaring the epidemic of international concern.

China's National Health Commission said 830 cases had been confirmed so far and 25 people had died as of Thursday. Most of the cases are in the central Chinese city of Wuhan, where the virus is believed to have originated late last year.

Non-fatal cases have been found in at least seven other countries.

Health officials fear the transmission rate could accelerate as hundreds of millions of Chinese travel at home and abroad during week-long holidays for the Lunar New Year, which begins on Saturday.

Nonetheless, it was a "bit too early" to consider the outbreak a "Public Health Emergency of International Concern," WHO Emergency Committee panel chair Didier Houssin said after the body met in Geneva. Such a designation would have required countries to step up the international response.

"Make no mistake, though, this is an emergency in China," said WHO chief Tedros Adhanom Ghebreyesus.

"It has not yet become a global health emergency. It may yet become one," he said.

• Countries with confirmed cases of coronavirus
• China puts millions on lockdown at virus epicenter

Scrambling to contain the outbreak, the local government in Wuhan, a city of 11 million people in Hubei province, suspended most transport on Thursday, including outgoing flights, and people were told not to leave. Hours later, neighboring Huanggang, a city of about 7 million people, announced similar measures.

"The lockdown of 11 million people is unprecedented in public health history," said Gauden Galea, the WHO's representative in Beijing.

The organization said, however, that it was not yet recommending any broader restrictions on travel or trade.

The previously unknown virus strain is believed to have emerged from illegally traded wildlife at an animal market in Wuhan.

It has created alarm because there are a number of unknowns surrounding it. It is too early to know just how dangerous it is and how easily it spreads between people.

There is no vaccine for the virus, which can spread through respiratory transmission. Symptoms include fever, difficulty breathing and coughing.