The head of the World Health Organization said on Tuesday that the global mortality rate for Covid-19, the disease caused by the new coronavirus, was 3.4 percent.

Tedros Adhanom Ghebreyesus, the organization’s director general, said in a news conference in Geneva that Covid-19 is deadlier than the seasonal flu, but does not transmit as easily.

“Globally, about 3.4 percent of reported Covid-19 cases have died,” said Dr. Tedros. “By comparison, seasonal flu generally kills far fewer than 1 percent of those infected.”

The estimate most likely takes into account the growing number of infections being recorded outside China, mostly in South Korea, Iran and Italy.

“While many people globally have built up immunity to seasonal flu strains, Covid-19 is a new virus to which no one has immunity,” meaning more people can be infected and some will suffer severe illnesses, said Dr. Tedros. The coronavirus does not transmit as efficiently as the flu but “causes more severe disease,” he added.

When the coronavirus crisis was concentrated in Wuhan, the Chinese city where the new virus was first found, the W.H.O. said that the mortality rate of the disease ranged from 0.7 percent outside of Wuhan to as high as 4 percent inside the city. The organization also said that the epidemic would affect different countries in different ways.

Data from the Chinese government shows that the mortality rate in that country is about 3.7 percent, with most deaths reported in Wuhan and the surrounding province of Hubei.

Dr. Tedros added on Tuesday that the disease can be contained, but warned that “rising demand, hoarding and misuse” of medical supplies such as masks could compromise the world’s ability to fight the outbreak, and he recommended a 40 percent global increase in the production of such supplies.