Meanwhile 60 more cases were confirmed on a cruise ship docked in Japan, and the UK declared that the virus constituted a serious and imminent threat to public health.
“There have been some concerning instances of onward 2019nCoV spread from people with no travel history to [China],” Ghebreyesus tweeted, using the virus’s provisional scientific name.
“The detection of a small number of cases may indicate more widespread transmission in other countries; in short, we may only be seeing the tip of the iceberg.”
On Monday, members of a WHO expert mission flew to China to help coordinate the response to the crisis, which has infected more than 40,000 people and killed at least 908. The country reported 97 deaths on Sunday, its largest toll in a single day since the outbreak was detected in December.
The Guardian report that more than 3,000 new cases had been reported over the previous 24 hours, raising the number of infections to 40,171. The increase follows a sharp decline in new cases reported on Sunday – fewer than 2,700, which led to optimism that prevention methods such as a strict quarantines were working.
Around the country, workers began trickling back to offices and factories as the government eased some restrictions on work and travel. In Beijing, roads were busier than in recent weeks but normally packed trains remained virtually empty. The few commuters on the street or using public transport were wearing face masks. Many companies have asked their staff to work from home.
Authorities had told businesses to add up to 10 extra days on to lunar new year holidays that had been due to finish at the end of January. The epidemic has caused huge disruption in China. Usually teeming cities have become ghost towns during the past two weeks as Communist party rulers ordered virtual lockdowns, cancelled flights, closed factories and shut schools.
The southern city of Guangzhou said it would resume public transport from Monday. Hubei province, hardest hit by the crisis, remains in lockdown, with train stations and airports shut and roads sealed off.
Despite government efforts to soothe the public about returning to work, some Chinese people have expressed concern.
“Of course we’re worried,” said a 25-year-old man in a beauty salon in Beijing, which reopened on Monday. He said the salon takes the temperature of all customers and asks them to wash their hands.
Others were relieved to leave their homes after weeks of self-quarantine. “Because going to work is normal life. Every day that I don’t go out and stay at home, I feel like people are going to die,” one commentator on Weibo said.
Volkswagen said while some of its factories would reopen on Monday, others had delayed production for another week. Toyota has extended the closure of its Chinese plants to 16 February.
Outside the mainland more than 350 infections have been reported in nearly 30 places. There have been two deaths: one in the Philippines and the other in Hong Kong.
British authorities said on Monday that four more patients had tested positive, bringing the total number of UK cases to eight. The development came as the government declared the outbreak a serious and imminent threat to public health, a step that gives authorities additional powers to fight the spread of the virus.
Sixty-six new infections have been confirmed on board the Diamond Princess ship off the coast of Japan, the ship’s operator said. Quarantined passengers posted on social media that many were feeling depressed as a result of their confinement, which began on 3 February after a man who disembarked in Hong Kong was diagnosed with the virus.
While the virus’s spread outside China has appeared to be slow, Ghebreyesus warned it could accelerate.
“Containment remains our objective, but all countries must use the window of opportunity created by the containment strategy to prepare for the virus’s possible arrival,” he said.
A team of international experts led by the WHO is heading for Beijing to help investigate the epidemic.
But it has taken nearly two weeks to get government approval on its composition, which was not announced, other than to say that the WHO veteran Dr Bruce Aylward, a Canadian epidemiologist and emergencies expert, was leading it.