A man accused of groping a female commuter threw Tokyo's busy rail network into disarray over the weekend after he jumped onto the tracks and ran away to elude capture, police said.

The man, who was described as being about 50 and clad in a T-shirt and trousers, jumped onto the tracks at Shinagawa Station and ran away.

He disrupted train traffic, causing delays in 42 trains, sometimes for as long as 26 minutes, affecting an estimated 27,000 commuters.

Police said that at about 6:15 p.m. Sunday night the man got onto a JR Yamanote Line train at Gotanda Station and thrust himself from behind into the rear of a woman in her 20s. When the train arrived at Shinagawa Station two stops away, the woman grabbed a station attendant and told him that the man was a groper. The man jumped onto the tracks and ran away.