A small can and a plastic bottle containing suspicious liquid left at a Tokyo subway station caused a terrorism scare Tuesday as Japanese security personnel stood on high alert for the Group of Eight summit, officials said.

At least 20 policemen and six fire engines, along with chemical weapons experts, rushed to the subway station near major hotels and government offices in the Japanese capital after a security guard found the objects just outside a ticket gate,Tatsuya Edakubo, a spokesman for the Tokyo Metro Company, said.

But after close examination, the liquid inside the bottle turned out to be detergent, and the can contained only soap — both accidentally left behind by a janitor at the station, Edakubo said.

The area was closed off for about 30 minutes during the evening rush hour, he said.

"It turned out there was nothing harmful," Edakubo said of Tuesday's incident. "Our security guard took extra caution because of the G-8 summit."

As with other mass transit operators across the country, the Tokyo Metro has been on special alert since June 10, sealing lockers, removing garbage bins and suspending use of vending machines at all stations.

The metro also mobilized about 1,700 employees to step up security at stations and on trains.

But at New Chitose Airport near the venue of the G-8 summit in northern Hokkaido, police arrested a Japanese man over an alleged bomb threat Tuesday on a domestic flight for Tokyo just before takeoff, a prefectural police official said on condition of anonymity, citing policy.

The 69-year-old suspect did not carry explosives and told investigators he was joking and had nothing against the G-8 summit, the police official said.