First robot marathon kicks off in Osaka, Japan

Video caption, Organisers say the race is a test of durability not speed

Five knee-high androids have crossed the starting line in the world's first marathon for two-legged robots.

The contest is being held in the Japanese city of Osaka.

The contestants are expected to take four days to complete the course, which involves 423 laps of an indoor track.

Operators are allowed to change the robots' batteries and motors but if the machines fall over they must get up by themselves.

The race is being organised by local authorities and a local robotics firm, which hopes the marathon will become an international event in the future.

Spectators turned out on Thursday to watch the start of the robots' 26-mile (42km) journey.

The toy-sized contestants waved and limbered up before the race got under way.

Organisers say they expect the race to be won not by the fastest robot but by the one that can withstand the most wear and tear.