A train crashed into a school minivan at a level-crossing in the Belgian town of Buggenhout on Tuesday, killing four people including two special needs pupils, authorities said.

As well as the 12- and 15-year-old students, the crash killed the driver aged 49 and a chaperone aged 27, said the local prosecutor’s office which opened an investigation.

“What could have been a beautiful spring morning suddenly turned into a pitch-black day,” East Flanders Provincial Deputy Kurt Moens told news outlet VRT NWS.

At the scene, a white minivan lay on its side near the track, its front badly crumpled.

Police spokesperson An Berger said the crossing’s safety barriers were down when the accident happened.