"A large indoor rally with 19-20,000 people is a huge risk factor today in Tulsa, Oklahoma," Tulsa City-County Health Department director Bruce Dart told the Tulsa World. "I want to make sure we can keep everyone in that building safe, including the president."
Mr Trump already delayed what will be his first official campaign rally since March by one day after an outcry of his original plan to hold the event on Friday. June 19 is also known as Juneteenth, which is recognised as a day commemorating the end of slavery in the United States.
Mr Dart's concern comes after Tulsa County's seven-day average of coronavirus cases climbed from 24.9 on 7 June to 51.4 seven days later.
"I think it's an honour for Tulsa to have a sitting president want to come and visit our community, but not during a pandemic. I'm concerned about our ability to protect anyone who attends a large, indoor event, and I'm also concerned about our ability to ensure the president stays safe as well," Mr Dart told the newspaper.
"COVID is here in Tulsa, it is transmitting very efficiently. I wish we could postpone this to a time when the virus isn't as large a concern as it is today," he added.
The Tulsa health official raised concerns because "people are not staying home now, they're out and about.
"I completely understand that, staying closed just wasn't feasible economically and from an emotional, physical perspective," Mr Dart added. "So if we're going to be out, we shouldn't be in enclosed spaces and we shouldn't have extended contact with other people because that's where the risk lies."
As Mr Dart sounds alarms, Mr Trump and his campaign manager are boasting about the event, making it less likely it will be moved. A campaign spokeswoman had not yet responded to a request for a reaction to Mr Dart's concerns.
"Almost One Million people request tickets for the Saturday Night Rally in Tulsa, Oklahoma!" Mr Trump tweeted on Monday morning.
The population of Tulsa County is around 651,500. The Trump campaign has not released any data supporting the president's claim.
Mr Trump did not mention Mr Dart in another morning tweet in which he dug in on his plans to begin holding large campaign rallies even amid the ongoing pandemic.
"The Far Left Fake News Media, which had no Covid problem with the Rioters & Looters destroying Democrat run cities, is trying to Covid Shame us on our big Rallies. Won't work!" the president wrote.
Mr Trump's tweets came a day after his 2020 campaign manager, Brad Parscale, bragged that the Tulsa rally had landed the re-election organisation its "biggest data haul and rally signup of all time by 10x."
He also claimed in that Sunday tweet that the event had "passed 800,000 tickets."
"Saturday," he wrote, "is going to be amazing!"
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