A witness who saw a man suffer a massive electric shock on the railway in Leeds said it was like a "firework going off".
The 21-year-old is fighting for life after he came into contact with overhead power lines - carrying up to 25,000 volts - having climbed a gantry next to the tracks close to Leeds bus station at about 3.30pm on Tuesday.
Police say initial reports that he had scaled the stanchion after being chased by security guards are thought to be incorrect.
But it is believed the man, who has no fixed address, was seen acting erratically before the incident.
A 31-year-old man, who did not want to be named, was waiting to pick his father in law up from the nearby Mecca Bingo when it happened.
He said: "I heard some people shouting then I looked over and saw the guy. He had climbed up this pole and he must have slipped and fell onto the wires.
"There was a big spark and a bang. It was like a massive firework going off.
"No-one could help him - he was being electrocuted. There were school kids screaming and shouting.
"After about a minute and a half he stopped moving."
The man was taken to hospital with massive burns and remains in a critical condition.
A British Transport Police spokeswoman said: "He has been transferred to the specialist burns unit at Pinderfields Hospital overnight where he remains in a critical condition.
"Officers have spoken to witnesses at the scene and examined CCTV covering the area and are not treating the incident as suspicious."
There was a huge emergency services response involving police, firefighters and paramedics and roads in the area were partially closed while initial investigations were conducted.
Commuters were hit by severe delays to trains into and out of Leeds central station, especially those on the popular Northern Rail and Trans Pennine Express services.
A Network Rail spokeswoman later thanked travellers for their patience.