Three Chinese cities are now in lockdown as authorities attempt to limit the spread of a deadly coronavirus.

A total of 20 million people are believed to have been impacted by the decision, with a number of major public events also cancelled.

Authorities banned transport links from Wuhan, the capital of Hubei province, on Thursday, as well as the nearby central cities of Huanggang and Ezhou.

Buses, subways and ferries in and around the cities have been suspended, while the airport and train stations have been closed to outgoing passengers.

Authorities in Beijing have also cancelled events including two well-known lunar new year temple fairs.

There have been 634 confirmed cases of the coronavirus, from the same family of viruses that gave rise to Sars.

Officials worry the lunar new year holiday, when hundreds of millions of Chinese will crisscross the country, will exacerbate an outbreak.

Cases have also been reported in the United States, Taiwan, South Korea, Thailand, Japan, Macau and Hong Kong.

Chinese authorities have confirmed 95 patients remain in critical condition.

Seventeen people have died since the virus was detected in late December, all of them in Wuhan.

Image: Xiao Yijiu/Xinhua News Agency/PA Images