But their statements also reinforced how much efforts to quantify the epidemic remain little more than rough estimates.

Among people who catch seasonal flus, about 0.1 to 0.2 percent die from the illness, though the number varies widely from year to year, depending on the strain of the virus and other factors. It has been apparent since January that the new virus had a significantly higher fatality rate — though lower than those of other coronaviruses like SARS and MERS.

“Globally, about 3.4 percent of reported Covid-19 cases have died,” Dr. Tedros Adhanom Ghebreyesus, the W.H.O.’s director general, said on Tuesday at a news conference in Geneva.

But the figure came loaded with caveats. Experts, including those at the W.H.O., say that when more is known about the epidemic, the death rate will be considerably lower.

The death rate Dr. Tedros cited does not include mild cases that were not detected because people did not seek medical attention. And it primarily reflects the experience in Wuhan, the Chinese city where the epidemic began — and where the numbers soared before China’s medical systems had gathered the knowledge and marshaled the resources to fight it.

Earlier estimates of the mortality rate in China had been closer to 2 percent.

Dr. Bruce Aylward, who is leading the W.H.O.’s coronavirus efforts, said he expects that ultimately, it will turn out to be between 1 and 2 percent. And it could be below 1 percent, according Dr. Anthony S. Fauci and Dr. H. Clifford Lane, of the National Institute of Allergy and Infectious Diseases, and Dr. Robert R. Redfield, director of the C.D.C.

The extent and mortality of the epidemic will not be known with great accuracy until a reliable test is developed for the antibodies present in people who have been infected, and that test is administered to large numbers of people.