The airport expects nearly 237,000 people to fly in or out on Monday, about 25% more than on a normal day.
The arrivals will include 335 athletes, the airport said in a statement. Athlete arrivals are expected to peak on July 24, with more than 1,200 competitors due on that day.
The arrivals begin amid a security snafu, as the government prepares to call in 3,500 military personnel because the security contractor says it does not expect to have enough staff in place.
G4S, the contractor, admitted on Wednesday that it would not be able to provide more than 10,000 security staffers by the time the Olympics begin.
Sports Secretary Jeremy Hunt said Sunday it should be no surprise that some contractors were unable to meet their commitments.
“It’s completely normal that you’re going to find some contractors on a project of this size who aren’t going to be able to deliver what they promised,” he said on the BBC’s “The Andrew Marr Show.”
He praised the contractor as being “honorable” for having admitted the problem, apologizing and covering the costs of bringing in military personnel.
And he reiterated that the government learned only last week that G4S would not meet its commitment.
“Management told us right up until last week that everything was on track,” Hunt said.
The contractor said Saturday it stands to lose up to $77 million after failing to recruit enough staff.
The airport, meanwhile, said Monday it is deploying more than 500 volunteers who speak 20 languages among them to welcome athletes and officials.
Immigration desks will have extra staff, the airport said, amid fears of long lines to get into the country.
The Games start on July 27.