Suggesting that smaller campaign crowds indicated the Democrat was less popular with voters, Mr Trump said in North Carolina on Wednesday that Mr Biden “can't fill them up”.
Thousands have packed into similar events over several months, as Mr Trump and his supporters eschewed masks, social distancing, and government recommendations.
Mr Biden, who dominates the president in national opinion polls, has meanwhile held a limited number of in-person events, as his campaign adhered to coronavirus measures.
Still, both Mr Trump and his supporters have sought to compare the two candidate’s campaign events over several months, whilst the United States’ death toll surpassed 220,000.
“You couldn’t catch Covid no matter what you did,” said Mr Trump on Wednesday, as he recalled a conversation with police about crowds at a previous campaign event.
“He said ‘we got so many people, we’re worried about it [a stampede]’. I thought that was for cattle, right? He said stampede”, the president told supporters.
“Can you imagine, now, Joe doesn't have that problem. He has about four or five circles. They can’t fill them up,” continued Mr Trump, as he went on to mock socially-distanced crowds, and drew circles in the air.
He added: “You know I'm a perfectionist. It’s beautiful those circles, they’re very far away from each other.”
The president’s criticism came as Jill Biden, the Democratic presidential nominee’s wife, said in an interview on Wednesday that Mr Trump and his supporters were “irresponsible”.
“It’s totally irresponsible that people are going to these [Trump] rallies and they’re not wearing masks, they're not social distancing," Dr Biden told The View. "It's irresponsible and people will die because of this”.
Public health authorities across the US have so far traced dozens of positive coronavirus cases to Trump rallies.