The World Health Organization upgraded its coronavirus risk assessment to "very high" on Friday as cases of the novel coronavirus COVID-19 disease continue to increase and in more countries.

The WHO said on Friday that it had received reports of a total of 4,351 cases in 49 countries, and 67 deaths, outside China.

Denmark, Estonia, Lithuania, the Netherlands and Nigeria had all reported their first cases in the 24 hours before Friday's press conferences in Geneva. All the cases have links to Italy.

"The continued increase in the number of cases, and the number of affected countries over the last few days, are clearly of concern," said the WHO's Director-General Tedros Adhanom Ghebreyesus.

He said that WHO epidemiologists have been monitoring these developments continuously. "We have now increased our assessment of the risk of spread and the risk of impact of COVID-19 to very high at a global level," he said.

According to the WHO, most cases can still be traced to known contacts or clusters of cases. It does not see evidence as yet that the virus is spreading freely in communities.

"As long as that's the case, we still have a chance of containing this virus, if robust action is taken to detect cases early, isolate and care for patients and trace contacts," Tedros said.

"The key to containing this virus is to break the chains of transmission."

Tedros said that work is progressing on vaccines and therapeutics. More than 20 vaccines are in development globally, and several therapeutics are in clinical trials.

"We expect the first results in a few weeks," he said.

He cautioned that people can still take action to protect themselves, despite the lack of a vaccine.

"There are things every individual can do to protect themselves and others today," he said, citing basic things such as washing hands regularly, cleaning surfaces regularly with disinfectant, being well informed on COVID-19, avoiding travelling with a fever or cough, not coughing or sneezing into clothing, and for people over 60 to take extra precautions.

Michael Ryan, executive director of the WHO's Health Emergencies Program, repeated at the press conference that it is not accurate to use the word "pandemic".

"If we say there is a pandemic coronavirus, we are essentially accepting that every human on the planet will be exposed to that virus. The data does not support that," he said.

"China has clearly shown that's not necessarily the natural outcome of this event if we take action, if we move quickly, if we do the things we need to do. That does not need to be the history of this event,"

He emphasized that if countries don't take action, don't move quickly and don't get ready, "that might be a future that people have to experience and endure".

"So much of the future of this epidemic is not in the hands of the virus. A lot of the future of this epidemic is in the hands of ourselves," he said.

Maria Van Kerkhove, technical lead with the program, said there is a lot that countries can learn from China in dealing with COVID-19.

Kerkhove, who just returned from a two-week trip to China, said lessons learned can be useful for low-income and high-income countries, low-incidence and high-incidence areas, as well as areas with migrant populations.