The World Health Organization says it will decide on Thursday whether to declare a global emergency over the outbreak of a new flu-like virus spreading from China.

If it does, it will be only the sixth international emergency to be declared in the last decade. These include the ongoing Ebola outbreak in Congo and the Zika virus in the Americas in 2016.

"The decision is one I take extremely seriously," WHO director-general Tedros Adhanom Ghebreyesus said, adding that he was only prepared to make it with the appropriate amount of consideration and information "in an evolving and complex situation."

He was speaking after the WHO held a day-long meeting of an independent panel of experts in Geneva on Wednesday.

WHO defines a global emergency as an "extraordinary event" that constitutes a risk to other countries and requires a co-ordinated international response.

Didier Houssin, chair of the emergency committee, was asked what gave the panel pause for making a recommendation.

"It was the question of assessment of severity and transmissibility," Houssin said. Information provided by Chinese authorities was too imprecise to make a recommendation about declaring an emergency, he added.

Watch | Chinese city at centre of outbreak locked down

The Chinese city where the new coronavirus started, Wuhan, has been put under quarantine while health officials are preparing a global response. 2:16

Dr. Peter Horby, a professor of emerging infectious diseases at Oxford University, said there were three criteria for an outbreak to be declared an international emergency:

The outbreak must be an extraordinary event.

There must be a risk of international spread.

A globally co-ordinated response is required.

Deaths from China's new coronavirus virus rose to 17 on Wednesday with more than 570 cases confirmed, increasing fears of contagion.

The coronavirus strain previously unknown to scientists was thought to have emerged from an animal market in the central city of Wuhan, with a case now detected as far away as the United States.

Wuhan is closing its transport networks and advising citizens not to leave the city, state media reported on Thursday.

Bus, subway, ferry and long-distance passenger transportation networks will be suspended from 10 a.m. local time on Jan. 23, and the airport and train stations will be closed to outgoing passengers, state TV said.

Public health actions do not begin at the declaration of a public health of emergency of international concern. These actions are already well underway - <a href="https://twitter.com/DrMikeRyan?ref_src=twsrc%5Etfw">@DrMikeRyan</a><br> <a href="https://twitter.com/hashtag/coronavirus?src=hash&ref_src=twsrc%5Etfw">#coronavirus</a> —@WHO

The official Xinhua News Agency also asked people not to leave the city without specific reasons.

Tedros commended China's decision to close transport in Wuhan, saying it helps the country contain the outbreak not only within China but also minimizes the chance of spread elsewhere.

With the first confirmed case in North America, our panel of doctors discuss whether Canadians should be worried about the new coronavirus and what they should be doing to protect themselves. 9:54

Most of the cases are in Wuhan and surrounding Hubei province, but dozens of infections have popped up this week around the country as millions travel for the Lunar New Year holiday, one of the world's largest annual migrations of people.

Thailand has confirmed four cases, while the United States, Taiwan, South Korea and Japan have each reported one.

The European Centre for Disease Control and Prevention said in a risk assessment that further global spread of the virus was likely.

Officials said it was too early to compare the new virus with SARS and Middle East respiratory syndrome (MERS), in terms of how lethal it might be. They attributed the spike in new cases to improvements in detection and monitoring.