The director-general of the World Health Organization on Tuesday said there was a "window of opportunity" for the international community to act on combatting a new viral outbreak emerging from China's central Hubei province.

While China was taking "strong measures" to stop the outbreak from spreading, the rest of the world should work on preventing a further spread and controlling it, Tedros Adhanom Ghebreyesus said.

He was speaking in Geneva where he briefed member states on the current situation regarding the virus.

Meanwhile, Britain has urged all its citizens in China to leave "if they can" to avoid coronavirus as health officials announced the disease has now infected 20,000 people worldwide.

It follows similar advice to US citizens, and comes after Hong Kong sealed all but two border crossings in a bid to contain the outbreak.

International commercial flights have been suspended to many parts of China, and domestic travel all but shut down.

"We now advise British nationals in China to leave the country if they can, to minimise their risk of exposure to the virus," UK foreign secretary Dominic Raab said on Tuesday. "Where there are still British nationals in Hubei province who wish to be evacuated, we will continue to work around the clock to facilitate this."

The advice came as mobile phone video emerged from Wuhan, China apparently showing a hospital overhwelmed with patients and bodies. Fang Bin, a 47-year-old seller of traditional clothes, said he visited No. 5 Hospital in Wuhan on Saturday and recorded the scenes before passing them to the Associated Press.

In Europe, hundreds of evacuees from the the city of Wuhan, where the outbreak began, were still being held in quarantine countries including Italy, France, Poland and the UK.

Earlier, China unveiled a new 1,000-bed hospital in Wuhan that was completed in just 10 days, with a second 1,500 bed hospital to be opened soon.

Novel coronavirus (2019-nCoV) has now infected well over than 20,000 people worldwide. China's health commission said on Tuesday that 425 people had died of the virus in the country.

Holiday camp

Dozens of Italians and Poles repatriated from the Chinese city of Wuhan have been quarantined over fears they may have contracted the coronavirus.

Italy's evacuation flight landed at a military airport near Rome on Monday - bringing 56 people home - while 30 people from Poland landed Sunday night. Both groups will spend two weeks in quarantine.

A total of 254 Europeans arrived in France on Sunday from Wuhan, where the deadly virus was first detected. They are now in quarantine in France — at a holiday camp near Carry-Le-Rouet or a firefighters' training centre near Aix-en-Provence — or have travelled on to their home countries.

The European Centre for Disease Control (ECDC) said authorities in Germany had confirmed another case on Sunday — a person who had close contact with a visitor from China.

Across Europe, confirmed cases now stand at 12 in Germany, 6 in France, 2 each in Italy, Britain and Russia and 1 each in Finland, Spain, Sweden and Belgium.

European cases include student and tourists

Beijing has criticised a decision by the United States to bar entry to most non-nationals who have visited China in the past two weeks, saying it contradicted the WHO’s appeal to avoid travel bans.

Other countries to have taken similar measures include Australia, Japan, Singapore and the Philippines.

The WHO said it was especially concerned that some cases outside China involved human-to-human transmission.

“Countries need to get ready for possible importation in order to identify cases as early as possible and in order to be ready for a domestic outbreak control, if that happens,” WHO representative in Beijing, Gauden Galea, told AP.

One of the first two people to test positive for coronavirus in the UK is a student at the University of York. The university said in a statement that the risk of infection is low and that the student and another member of their family are being treated at a specialist unit in Newcastle.

Elsewhere in Britain, 83 British nationals evacuated from Wuhan were on their third day of a two-week quarantine at a hospital in Wirral while 27 non-UK nationals were at Brize Norton RAF base in Oxfordshire.

There have been eight cases of human-to-human transmission in four countries outside China: Germany, Japan, Vietnam and the US.

France revealed its sixth case of coronavirus on January 30 — a Paris doctor who'd come back from China.

In Finland, two cases have been reported including a Chinese tourist found to be infected with the virus at a hospital in Lapland, according to health authorities. They said the tourist was from Wuhan and that a further 15 people may have been exposed.

What's the situation in China?

In Hubei, bustling streets, shops, restaurants and other public spaces in the city were eerily empty as authorities put more than a dozen cities on lockdown.

The city of Wuhan, where the outbreak originated, has admitted the first patients to the new hospital, while construction crews continue to work around the clock on the second facility.

Police, SWAT teams and paramilitary troops guarded the city's train station, where metal barriers blocked the entrances.

The cities of Beijing, Shanghai, Xian and Tianjin have suspended long-distance coach services, as well as the vast province of Shandong.

As a symbol of the concern that has gripped China, the authorities have announced the closure of sections of the famous Great Wall, as well as the Disneyland resort site in Shanghai.

Hong Kong's leader Carrie Lam announced on Tuesday that all rail links to mainland China will be closed starting Friday, in order to stop the contagion. This includes both the high-speed rail station and the regular train station.

Mongolia already closed its vast border with China and North Korea said it was strengthening quarantine measures.