President Donald Trump has cancelled the pre-election Republican party convention in Florida, blaming the coronavirus "flare-up".
"It's not the right time for that," he said, adding that he would still give a convention speech in a different form.
It comes as the number of cases of Covid-19 in the US passed four million.
Part of the convention will go ahead in North Carolina, where Mr Trump will be formally nominated as the Republican presidential candidate.
The event, shortened to half a day, will be held on 24 August in the city of Charlotte, the original venue for the convention.
Mr Trump switched the location to Jacksonville, Florida after the Democratic governor of North Carolina insisted in May on limiting the crowd size at the convention, on the grounds of social distancing.
What did the president say?
Mr Trump told Thursday's White House coronavirus briefing that safety was his main concern in calling off the four-night convention.
"It's a different world, and it will be for a little while," the president said, adding that he "just felt it was wrong" to put potentially tens of thousands of attendees at risk.
"We didn't want to take any chances," he told reporters. "We have to be careful and we have to set an example."
The sheriff in Jacksonville warned this week the city was not ready for next month's event.
Traditionally four days long, the national nominating conventions of both Republicans and Democrats are the highlights of the internal party contests in the lead-up to the November polls.
There, delegates from across the country vote for their preferred candidate. Historically these events attracts tens of thousands of people and are held in a festive-like atmosphere.
Florida - a state crucial to the president's re-election hopes - is behind only California and New York in total cases.
Opinion polls suggest Mr Trump is facing an uphill battle for a second term in office amid criticism of his handling of the pandemic.
What will happen at the Charlotte convention?
Donald Trump is the sole Republican candidate, after his last remaining challenger, former Massachusetts Governor Bill Weld, dropped out in March.
At the convention, some 2,472 delegates - though it is unclear how many will actually attend this year because of the pandemic - will vote for Mr Trump as their nominee, officially launching his re-election bid. The party will also unveil its platform, or manifesto.
In normal times, thousands of journalists, party grandees, lawmakers and guests would attend the convention.
This year it will be abridged. Historically the vice-presidential nominee addresses the gathering a day before the presidential candidate's acceptance speech marks the culmination of the event. Mr Trump's penchant for limelight and rallies though will ensure it is anything but subdued.
What's the reaction?
Democratic Party officials taunted the president over his announcement. They are going to hold an almost entirely virtual convention in August in Milwaukee, Wisconsin, where Mr Trump's challenger, Joe Biden, will formally accept the party nomination.
A Democratic strategist involved in the preparations said: "I wonder who will have the better convention - the party who recognised the limitations early on and have been planning for a mostly virtual/digital television production to capitalise on a prime-time audience of millions, or the clowns who keep moving theirs from place to place and have no concrete plan a month out."
In a "socially-distanced" conversation released on Thursday, Mr Biden and his former boss, ex-President Barack Obama, poured scorn on Mr Trump's deflection of blame in March. At that time Mr Trump said: "I don't take responsibility at all" when asked about delays in Covid-19 testing.
"Can you imagine standing up when you were president, saying, 'It's not my responsibility?'" said Mr Biden, the former vice-president, in their chat recorded last week.
Mr Obama replied: "Those words didn't come out of our mouths when we were in office."
What's the national picture?
As well as passing four million confirmed cases on Thursday, the US has recorded more than 144,000 deaths linked to Covid-19.
On Wednesday, California passed New York - the former epicentre of the US outbreak - for the most confirmed cases with 409,000.
On the same day, Missouri, North Dakota and West Virginia all broke their records for the most new cases in a 24-hour period.
Alabama, Idaho and Texas also reported new record highs in daily deaths.
Across the US on Wednesday, a total 69,707 new virus cases were recorded.
Republicans and Democrats in Congress are meanwhile negotiating a deal to pass a fifth economic stimulus package. The price tag for the previous four stands at $3tr (£2.4tr).