TOKYO - The world's first robot marathon is under way in western Japan, with five two-legged participants racing on an indoor track.

The race kicked off Thursday with the 1-foot (30-centimeter) -tall, battery-charged robots competing around a 110-yard (100-meter) racetrack. They will have to cover 26 miles (42 kilometers).

Japanese robot maker and event organizer Vstone Co. says the "Robo Mara Full" race in Osaka will demonstrate the machines' durability and maneuverability.

Vstone robots took an early lead, while two entrants by Osaka University of Engineering teams got off to a shaky start. The race is expected to last through Sunday.

Vstone CEO Nobuo Yamato hopes the event will become international in the future.