Long lines have formed outside an arena where President Donald Trump will hold his first rally since March, when the coronavirus blockade began in the U.S.
There are concerns that the event at the 19,000-seat Bank of Oklahoma Center in Tulsa could increase Covid-19's expansion.
Participants must sign a waiver protecting the Trump campaign from liability for any illness.
Hours before the rally, the campaign said six employees involved in organizing the test were positive.
On Friday, the Oklahoma Supreme Court dismissed an action calling for the social detachment guidelines to be followed.
The Trump campaign said that participants will have to undergo temperature checks before being allowed to enter the site – and that they will be given face masks.
More than 2.2 million cases of Covid-19 and 119,000 associated deaths have been reported in the United States, according to data from Johns Hopkins University.
The Trump re-election campaign demonstration will be one of the largest U.S. internal meetings since the start of the Covid-19 outbreak in the country.
Campaign officials said they had received more than a million ticket orders and that the president would speak inside the BOK Center, as well as on an outdoor stage set up nearby, to crowded crowds.
Supporters started lining up earlier this week for a chance to enter the arena, and 100,000 or more people are expected to gather in downtown Tulsa.
This week, the number of new cases of Covid-19 in Oklahoma has increased and local health officials fear the rally could become a "super-spreading" event.
There will be no social distance at the rally. And although masks are given to those present, the president will not be wearing one.
Participants must accept a disclaimer that "they voluntarily assume all risks related to exposure to Covid-19 and agree not to keep Donald J. Trump as President, Inc." responsible for any illness or injury.
In a Facebook post, Tulsa Mayor GT Bynum acknowledged that Tulsa residents were divided for being the first city to host this event.
"We do this as our positive cases of Covid-19 are increasing, but as long as our hospital capacity remains strong. Some think it is great, others think it is unwise. Regardless of where each of us falls on that spectrum, we will go through that as a community, "he wrote.
Political rallies are a source of inspiration and invigoration for Donald Trump. He draws energy from arenas full of enthusiastic supporters and uses his responses to the various riffs in his speeches, sometimes long and free-form, to feel what problems resonate with his loyal base.
For more than three months, as Covid-19 spread across the United States, the president has been without these emotional and strategic sounding boards. Now rallies are coming back, even as cases of the virus reach new record highs in many states and public health officials continue to warn of the dangers of large meetings.
With election day less than five months away, the president is charging this as the start of his run for re-election. Given that he carried out his official campaign launch in Orlando almost exactly a year ago, it may be better to see it as a reinitialization of a campaign that has struggled to establish itself, as the country has been plagued by pandemic and mass demonstrations against racism institutional and excessive police force.
The president is now charging his campaign around the slogan "The Great American Return". Given the recent turmoil and declining numbers from Trump's poll, he clearly hopes that the Tulsa rally will be the beginning of his own political renaissance.
There are also concerns among officials in Tulsa that there will be clashes between supporters and opponents of the president.
Emotions are still high after the murder of an unarmed black man, George Floyd, by the Minneapolis police last month, which sparked widespread protests against racism.
Mayor Bynum on Thursday declared a curfew covering the area around the BOK Center, citing the risk of "civil unrest". But on Friday, Mr. Trump announced that the curfew was raised for "our many supporters".
He also warned: "Any protester, anarchist, agitator, looter or slob who is going to Oklahoma, please understand that you will not be treated as in New York, Seattle or Minneapolis. It will be a very different scene!"
Trump planned to hold the rally on Friday. But he changed the date last week after learning that it fell on June 11, which marks the end of slavery in the United States.
The choice of location is also controversial. In 1921, Tulsa was the scene of a racial riot in which white crowds attacked blacks and companies.
At a peaceful thirteenth meeting in Tulsa on Friday, civil rights activist Al Sharpton said activists could "make America great" for everyone for the first time.