A delivery driver has died at a train depot after trying to help a teenager who was injured while playing on top of a train.
A witness saw five youths on the train at the Temple Mills Depot in Leyton, east London, at 1950 BST on Sunday.
He heard a bang, saw one of the youths on fire, then watched as an Asda driver walked across the car park to help.
It is not known if the man died of a heart attack or was electrocuted. Two teenagers were taken to hospital.
A post-mortem examination is being arranged to discover what killed the driver, 59, from Laindon in Essex.
It is thought one of the teenagers touched a 25,000-volt cable.
A 17-year-old from Leyton is being treated at Broomfield Hospital in Chelmsford for injuries to his right side and back and another youth had burnt his hands.
Police are taking witness statements from the other three teenagers.
A spokesman for British Transport Police said the incident showed how dangerous it was to play on the railway.
"It is only by good fortune that several young people are not now dead," he said.
"Tragically, one man has lost his life and our sympathies go to his family."