A 19-year-old Hamilton man was seriously ill in Waikato Hospital's intensive care unit last night after a stunt on rail tracks went wrong.
He has severe burns, and had surgery yesterday.
Police said they were called about 10pm on Wednesday after the youth climbed on top of train carriages on a section of rail line on Avalon Drive parallel to State Highway 1 at Te Rapa and received an electric shock.
They said the youth had not been drinking, but had decided to climb on the wagons in front of friends.
No charges had been laid.
Senior Sergeant Eddie Carr said an On Track investigator had been sent from Wellington.
"We'll be amassing all information from witnesses, On Track, and from scene examinations," he said.
"We need people to be aware of the danger of going near such high-voltage lines. I've heard of people being electrocuted by just getting close to them."
Toll Rail general manager Joe Garbellini said trespassers were a long-standing problem at the Te Rapa railway yards.
In 2002, Hamilton coroner Gordon Matenga recommended that Tranz Rail - which then owned the rail system - improve warning signs around the Te Rapa marshalling yards, after a 15-year-old boy lost his life there.
Troy Robert Jumeau received a 25,000-volt shock from overhead train wires after climbing on to a carriage, and died six days later.
In March 2003, Mr Matenga recommended that Tranz Rail consider building a continuous fence near houses on the eastern side of the yard.
He asked that a risk assessment be carried out on all its goods yards on the main trunk line where similar layouts existed.