Police remained at the scene on Monday morning
A 13-year-old boy has died at a railway maintenance site in Liverpool, after apparently being electrocuted by an overhead power line.
British Transport Police were called to the depot in Allerton, at 1700 BST on Sunday, after reports three youths had been seen inside.
Ch Supt Peter Holden said the dead boy had climbed on top of a disused train. The others had both suffered burns.
Officers are now investigating how the youths gained access to the site.
The scene has been cordoned off while the investigation is carried out and the boy's family have been informed.
Ch Supt Holden said it was "an extremely tragic incident".
"Three youths had been seen within the maintenance depot, and it would appear that they'd accessed the roof of a train that was in storage - so a disused train if you like - and unfortunately come into close contact with the overhead electrical lines," he told BBC Radio 5Live.
"It would appear that one of these has arced, resulting in the regrettable and unfortunate fatality of the 13-year-old youth.
"The overhead cable carries 25,000 volts of electricity and quite clearly when someone comes into close proximity the current can arc across."
Officers are investigating how the boys gained access
Ch Supt Holden said there were fences and warning signs around the site, which is used to store freight trains, and it was "as secure as it can be".
"The depot covers a large area with a large amount of perimeter fencing," he said.
"Because it's such a large area it wouldn't necessarily follow that these people would be easily detected once they'd gone into the depot.
"It's a large environment to fence off, but, obviously, the fences are there to keep people out."
The two other youths are now being treated in hospital for burns that are not thought to be life-threatening.
Ch Supt Holden said his colleagues did a lot of work in the Merseyside area to try to educate schoolchildren about the dangers of the railway environment.