But his intended show of political force amid a pandemic featured thousands of empty seats and new coronavirus cases on his own campaign staff.

Trump ignored health warnings to hold his first rally in 110 days - one of the largest indoor gatherings in the world during a coronavirus outbreak that has killed more than 120,000 Americans and put 40 million out of work.

Saturday's rally was meant to restart his re-election effort less than five months before the president faces voters again.

"The choice in 2020 is very simple," Trump said. "Do you want to bow before the left-wing mob, or do you want to stand up tall and proud as Americans?"

Trump unleashed months of pent-up grievances about the coronavirus, which he dubbed the "Kung flu," a racist term for COVID-19, which originated in China. He also tried to defend his handling of the pandemic, even as cases continue to surge in many states, including Oklahoma.

He complained that robust coronavirus testing was making his record look bad - and suggested the testing effort should slow down.

"Here's the bad part. When you do testing to that extent, you're going to find more cases," he said. "So I said to my people, 'Slow the testing down.' They test and they test."

"Speed up the testing," Trump's Democratic opponent, Joe Biden, tweeted later.

In the hours before the rally, crowds were significantly lighter than expected, and campaign officials scrapped plans for Trump to address an overflow space outdoors. When Trump thundered that "the silent majority is stronger than ever before", about a third of the seats at his indoor rally were empty.

Trump tried to explain away the crowd size by blaming the media for scaring people and by insisting there were protesters outside who were "doing bad things". But the small crowds of pre-rally demonstrators were largely peaceful, and Tulsa police reported just one arrest.

Before the rally, Trump's campaign revealed that six staff members who were helping set up for the event had tested positive for the coronavirus. Campaign communications director Tim Murtaugh said neither the affected staffers nor anyone who was in immediate contact with them would attend the event.

The president raged to aides that the staffers' positive cases had been made public, according to two White House and campaign officials who spoke on condition of anonymity because they weren't authorized to speak publicly about private conversations.

Trump also leaned in hard on cultural issues, including the push to tear down statues and rename military bases honoring Confederate generals following nationwide protests about racial injustice.

"The unhinged left-wing mob is trying to vandalise our history, desecrate our monuments, our beautiful monuments," Trump said. "They want to demolish our heritage so they can impose their new repressive regime in its place."

Trump also floated the idea of a one-year prison sentence for anyone convicted of burning an American flag, an act of protest protected by the First Amendment.

After a three-month break from rallies, Trump spent the evening reviving his greatest hits, including boasts about the pre-pandemic economy and complaints about the media. But his scattershot remarks made no mention of some of the flashpoints roiling the nation, including the abrupt firing of a US attorney in Manhattan, the damaging new book from his former national security adviser or the killing of George Floyd.

Large gatherings in the United States were shut down in March because of the coronavirus. The rally was scheduled over the protests of local health officials as COVID-19 cases spike in many states, while the choice of host city and date - it was originally set for Friday, Juneteenth, in a city where a 1921 racist attack killed as many as 300 people - prompted anger amid a national wave of protests against racial injustice.

But Trump and his advisers forged forward, believing that a return to the rally stage would re-energise the president, who is furious that he has fallen behind Biden in polls, and reassure increasingly anxious Republicans.

City officials had expected a crowd of 100,000 people or more in downtown Tulsa. Trump's campaign, for its part, declared that it had received over a million ticket requests. The crowd that gathered was far less than that.

Australian Associated Press