The pedestrian who died in Christchurch last night after being hit by a train was walking with friends at the time, police said.
The incident occurred around 8.50pm at the railway crossing on Factory Road, Belfast.
Police said early enquiries indicated the boy had been walking with two associates, one male and one female, when they crossed the rail crossing.
Detective Sergeant Richard Quested said the boy's two friends crossed the railway line, but he was struck by a north-bound freight train.
Witnesses said the crossing alarm bells were operating and barrier arms were coming down at the time of the incident.