WHO chief Tedros Adhanom Ghebreyesus said there had been "concerning instances" of transmission from people who had not been to China
People across China trickled back work on Monday after an extended Lunar New Year holiday as the government eased restrictions imposed to counter the coronavirus, but the World Health Organization (WHO) said the number of cases outside China could be just "the tip of the iceberg".
The death toll from the epidemic rose to 908, all but two in mainland China, on Sunday as 97 more fatalities were recorded - the largest number in a single day since the virus was detected in the city of Wuhan in December.
The Diamond Princess cruise ship with 3,700 passengers and crew onboard remained quarantined in the Japanese port of Yokohama, with 65 more cases detected, taking the number of confirmed case from the Carnival Corp-owned vessel to 135.
European stocks fell on concerns about the impact of the closure of factories in China, the world's second-largest economy, on supply chains for companies from Taiwan's iPhone-maker Foxconn to carmakers Kia Motors and Nissan
Across mainland China, 3,062 new infections were confirmed on Sunday, bringing the total number to 40,171, according to the National Health Commission (NHC). An advance team of international WHO experts was en route to Beijing to investigate the outbreak.
Wu Fan, vice-dean of Shanghai Fudan University Medical school, said there was hope the spread might soon reach a turning point.
"The situation is stabilising," she told a briefing when asked about the spread in Shanghai, which has had nearly 300 cases and one death.
But WHO chief Tedros Adhanom Ghebreyesus said there had been "concerning instances" of transmission from people who had not been to China.
"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," he said in Geneva.
The virus has spread to at least 27 countries and territories, according to a Reuters count based on official reports, infecting more than 330 people. The two deaths outside mainland China were in Hong Kong and the Philippines.
The death toll from the outbreak has now surpassed that of Severe Acute Respiratory Syndrome (SARS), which killed hundreds worldwide in 2002/2003.
Usually teeming cities have become virtual ghost towns after Communist Party rulers ordered lockdowns, cancelled flights and closed factories and schools.
Ten extra days had been added to the Lunar New Year holidays that had been due to finish at the end of January. But even on Monday, many workplaces remained closed and many people worked from home.
Few commuters were seen during the morning rush-hour on one of Beijing's busiest subway lines. All were wearing masks.
One Beijing government official, Zhang Gewho, said it would be be harder to curb the spread of the virus as people returned to work.
"The capacity of communities and flow of people will greatly increase and the difficulty of virus prevention and control will further rise," he said.
Hubei, the province of 60 million people that is the hardest hit by the outbreak, remains in virtual lockdown, with its train stations and airports shut and its roads sealed.
In Britain, the government said on Monday the number of confirmed coronavirus cases there had doubled to eight and it declared the virus a serious and imminent threat, giving it additional powers to isolate those suspected of being infected.
China's central bank has taken a raft of steps to support the economy, including reducing interest rates and flushing the market with liquidity. From Monday, it will provide special funds for banks to re-lend to businesses.
President Xi Jinping, who has largely kept out of the spotlight, leaving Premier Li Keqiang to take the public lead in government efforts to control the outbreak, said on Monday the government will prevent large-scale layoffs, Chinese state television reported.
Xi, who was shown on television inspecting the work of community leaders in Beijing, and wearing a mask as he had his temperature taken, also said China will strive to meet economic and social targets for the year.
He reiterated that China would beat the virus. One senior economist has said growth may slow to 5 percent or less in the first quarter.
More than 300 Chinese firms including Meituan Dianping, China's largest food delivery company, and smartphone maker Xiaomi Corp are seeking loans totalling at least 57.4 billion yuan ($8.2 billion), two banking sources said.
Apple's biggest iPhone maker, Foxconn, won approval to resume production in the eastern central Chinsese city of Zhengzhou, but only 10 percent of the workforce has managed to return, a source said. But the southern city of Shenzhen rejected a company request to resume work there.
Much remains to be determined about the virus, which has been linked to a market selling animals in Wuhan, the capital of Hubei province.
Scientists at Imperial College London published new estimates of an overall case fatality rate of 1 percent.
But they said that this could range from 0.5% to 4% and warned there was "substantial uncertainty" due to varying levels of surveillance and data reporting.