Eyewitnesses saw the youngster cross the level crossing when the Tongeren train had already arrived in the station. He was knocked down by a goods train that was coming from the other direction.
The emergency services were unable to revive him.
Police are now trying to establish what exactly happened.
The level crossing is destined for closure in a couple of years when a new fast tram will connect Hasselt and the Dutch city of Maastricht. The crossing was equipped with a conventional bell and not the new digital bell that the rail track operator is introducing.