China effectively quarantined 20 million people on Thursday in what is thought to be the largest ever operation of its kind as authorities mounted a desperate attempt to control the outbreak of the deadly coronavirus.

Authorities grounded flights, blocked roads and closed train stations to stop residents leaving Wuhan, the epicentre of the mystery disease, while restrictions were imposed on five further cities in Hubei province.

At least 18 people have died and 600 people are known to have contracted the virus that is thought to have come from a wholesale food market in Wuhan, a city of 11 million people.

Travellers arriving after the Wuhan ban went into effect on Thursday morning were met by police, SWAT teams, paramilitary guards and metal barriers at the high-speed train station. People booked on trips beyond the deadline were turned away.

Transport links were also being sealed off in the cities of Huanggang, Ezhou, Lichuan and Xiantao. Authorities in Huanggang have told residents not to leave and ordered entertainment venues, such as cinemas and internet cafes, to shut their doors.