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World Health Organization officials are holding a press conference Friday to update the public on the new coronavirus outbreak.

As of Friday, more than 31,000 cases of coronavirus have been reported in over two dozen countries, resulting in at least 636 deaths almost exclusively in China. The WHO declared the virus a global health emergency last week, a rare designation that helps the international agency mobilize financial and political support to contain the outbreak.

"There's still a lot we don't know," Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said Thursday.

While scientists have made progress in sequencing the virus's DNA and generally know how it is transmitted, he said they still don't know the source of the outbreak or its natural host. The agency also hasn't found a vaccine or treatment, "and we don't properly understand its transmissibility or severity," he said.

"To put it bluntly, we're shadow boxing," Tedros said Thursday. "We need to bring this virus out into the light so we can attack it properly."

WHO is convening a two-day global research and innovation forum next week to share research and ideas on how to combat the virus, he said.

On Wednesday, Tedros said that the number of confirmed cases grew by more than 3,100 over the previous 24 hours, which he said was "the most cases in a single day since the outbreak started" on Dec. 31. However, he emphasized that the overwhelming majority of cases are in China, and of those, 80% are in Hubei province, where the virus was first detected in the city of Wuhan.

"Our greatest concern is about the potential for spread in other countries with weaker health systems and who lack the capacity to detect and diagnose the virus," he said Wednesday. "We're only as strong as the weakest link."

"We cannot defeat this outbreak without solidarity. Political solidarity, technical solidarity, and financial solidarity," he continued.

Tedros also announced Wednesday that the WHO is requesting $675 million to fund its "strategy preparedness and response plan" for the next three months. He said the WHO has already tapped $9 million of funding from its contingency fund for emergencies.

[To see the latest updates on the coronavirus, visit CNBC's live updates here.]