"Some areas of our country are doing very well," Trump said at his first formal White House virus briefing since the end of April.
"Others are doing less well," the president said. "It will probably unfortunately get worse before it gets better."
He said there had been a "a concerning rise in (virus) cases in many parts of our South".
Trump urged Americans to wear face masks to help prevent the spread of the highly contagious virus, which has left more than 141,000 people dead in the United States.
"We are asking everybody that when you are not able to socially distance, wear a mask," he said.
"Whether you like the mask or not, they have an impact. They will have an effect and we need everything we can get."
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Trump said the goal is "not merely to manage the pandemic but to end it."
"The vaccines are coming and they're coming a lot sooner than anyone thought possible," he said.
Trump also repeated his assertion that the virus "will disappear".
"It will disappear," he said.
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