He appointed Vice President Mike Pence to oversee efforts to stem the virus’s spread in the United States, while seeking to play down the severity of the crisis in remarks to reporters.

He said that “the flu in our country kills from 25,000 people to 69,000 people a year,” contrasting it with the coronavirus, which has not yet killed anyone in the United States. But top health officials have warned that the virus will almost certainly spread in the country.

Both Democrats and Republicans have assailed Trump for his request of $2.5 billion in funding to combat the virus. Nancy Pelosi, the speaker of the House, called that request “long overdue and completely inadequate to the scale of this emergency.”

Pelosi criticized Trump for leaving “critical positions in charge of managing pandemics at the National Security Council and the Department of Homeland Security vacant,” and for attempting to cut funding to the Centers for Disease Control and Prevention.

In an appearance on MSNBC, Representative Donna Shalala, who served as health and human services secretary under President Bill Clinton, rejected the idea that Trump ought to be speaking about a health issue on television. “This is an anti-science administration,” she said. “The last person the American people trust is the president of the United States talking about science.”

But Trump asserted that his administration’s response to the spread of the virus has been excellent. Responding to reporters, he also said he would be open to restricting access to the United States from countries with high rates of infection with the virus.

The C.D.C. announced on Wednesday that a person in California had been infected but was not known to have recently visited a foreign country or had contact with a confirmed case. That could make it the first case of community transmission in the country.