TOKYO, July 8 (Reuters) - Tokyo's Haneda airport was shut down for two hours on Saturday after a man was found running across one of its runways, airport officials said, affecting scores of flights.

An infrared ray sensor system detected an "alien" object on the runway eaerly on Saturday and surveillance cameras spotted the man but then lost him, forcing the closure of the runway, an official said.

The man later turned out to be a 22-year-old part-time worker for a company cleaning airplanes, who told airport authorities that he had wanted to get closer to the sea.

"He said he was still not used to working and had wanted to go exercise near the sea," the official said.

Haneda airport, which serves mostly domestic and also some international flights, is next to Tokyo Bay.

The airport's other two runways were also closed from late Friday for construction work, and some 90 flights to and from Haneda were affected as a result.