DENVER -- A sub-contractor working on a runway at Denver International Airport was killed early Monday when he was hit by a sweeper driven by a DIA worker.

According to Denver police, the mishap occurred just before 5 a.m. on runway 16L. The runway is 12,000 feet long and the worker was killed on a far end of the runway where jets first touch down, leaving black rubber marks and tire pieces on the concrete.

The sub-contractor was cleaning rubber pieces off the runway when he was hit by a large sweeper driven by an employee of DIA.

"The man had apparently bent over to retrieve an item and could not be seen by the operator of the heavy equipment," said Detective John White.

The 46-year-old victim was employed Rampart Hydro Services, which is headquartered in Coraopolis, Pa., but was not identified. He is from Pennsylvania.

"They use use high-pressure water washers to blow that accumulated rubber off of the runway and then our crews go up and cleanup behind them," said DIA spokesman Chuck Cannon. "We normally send out one of our big runway brooms to sort of sweep up behind them, make sure there's no debris left on the runway."

The area where the accident occurred was blocked off by police and the sweeper and another large piece of equipment were stopped on the runway. The runway was reopened shortly after 11 a.m.

The DIA employee driving the sweeper and employees of the sub-contractor were advised to take time off for counseling.

The Occupational Safety and Health Administration is investigating the mishap, along with Denver Police.

The federal investigation is expected to last a month, 7NEWS reported.