LONDON (AFP) - The Foreign Office in London on Tuesday (Jan 28) warned British nationals against "all but essential travel" to mainland China due to a deadly novel coronavirus outbreak.

The ministry advised against all but essential travel to mainland China, not including Hong Kong and Macau, while continuing to warn against all travel to the worst-affected Hubei Province.

"If you're in this area and able to leave, you should do so," the Foreign and Commonwealth Office said.

"Due to increasing travel restrictions and difficulty accessing medical assistance, the FCO is working to make an option available for British nationals to leave Hubei Province.

"This may happen quickly and with short notice."

Britons were urged to make contact by 11am local time (11am Singapore time) on Jan 29 to register their wish to leave.

Officials estimate up to 200 citizens currently there will want to return to Britain.

The FCO said it may become more difficult for British nationals in other provinces to leave.

"The Chinese government continue to impose further restrictions on movement within China in response to the coronavirus outbreak," it said on its website.

"It may become harder over the coming weeks for those who wish to leave China to do so. If you feel that you may want to leave China soon, you should consider making plans to do so before any further restrictions may be imposed."

The news comes as almost 100 people in Britain have tested negative for the SARS-like virus.

The virus has so far killed more than 100 people.

The infection is believed to have originated in a wild-animal market in the central Chinese city of Wuhan.

In a development that could cause more jitters abroad, Japan and Germany reported the first confirmed cases of human-to-human transmission outside of China.

World financial markets outside Asia nevertheless rebounded following a global sell-off fuelled by the spread of the virus.