The World Health Organization (WHO) is concerned about the number of coronavirus cases with no clear epidemiological link, although the total number of cases outside China remains relatively small, its director general has said.

Cases with no clear link include those with no travel history to China or contact with a confirmed case, Tedros Adhanom Ghebreyesus said in a briefing.

There is also concern at the disease's ability to stay undetected in people who can unknowingly spread it to others. A 20-year-old woman travelled from Wuhan to a city 675km away where she infected five others, Chinese scientists said on Friday, despite showing no symptoms herself. 

"You had this patient from Wuhan where the virus is, traveling to where the virus wasn't," Dr William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, told Reuters.

"She remained asymptomatic and infected a bunch of family members and you had a group of physicians who immediately seized on the moment and tested everyone."

The scientists behind the report said if that's common, COVID-19 could be harder to control than previously believed.

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China has reported more than 76,000 cases to the WHO, including 2354 deaths. Worldwide there have been nearly 78,000 cases reported, with 2362 deaths, as of Sunday morning (NZ time). 

According to available data, the disease remains mild in 80 percent of coronavirus patients, and is severe or critical in 20 percent of patients, he said.

The virus has been fatal in 2 percent of reported cases.

The risk of death increases for older patients, Tedros said, adding there were relatively few cases among children.

Outside China, there have been 1200 cases in 26 countries, with eight deaths, Tedros said. That includes one confirmed case on the African continent, in Egypt, he said.

He called the reported decline in new cases in China welcome news but said it had to be interpreted very cautiously, adding, "It is far too early to make predictions about this outbreak"

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A WHO-led international team of experts, which has been on the ground in China for the past week, will travel to Wuhan, the epicentre of the virus outbreak, on Saturday.

"Our biggest concern continues to be the potential for COVID-19 to spread in countries with weaker health systems," Tedros said.

The WHO is calling for US$675 million to support countries, especially those which are most vulnerable, he said, adding it has identified 13 countries in Africa that are seen as a priority because of their links to China.

It has shipped more than 30,000 sets of personal protective equipment to several African countries, and is ready to ship almost 60,000 more sets to 19 countries in coming weeks, Tedros said.