A crash between a bus and a train travelling at high speed in northern Belgium killed four people, including two children aged 12 and 15, and injured five other children, officials said on Tuesday.

The injured children were hospitalised in serious condition, said Lisa De Wilde, spokeswoman for the East Flanders public prosecutor’s office. The collision happened at a level crossing during the morning rush hour near the town of Buggenhout, about 30km (20 miles) northwest of the capital, Brussels.

The minibus driver and an escort were killed along with two children, De Wilde said at a news conference. She said that the cause of the crash had not been established. Investigators were questioning witnesses and checking security camera footage.

“What we do know is that the barrier was closed and the red light was on,” she said.

A reporter at the scene said that the badly damaged bus lay toppled on its side, its front section crushed flat. Forensic experts in protective white suits and wearing gloves were taking photos of the scene. A forensics tent was erected nearby. The train was relatively unscathed.

The train was estimated to be travelling at about 120km/h (75mph) as it approached the crossing and had “no time to brake,” said Frederic Sacre, a spokesman for Belgian rail operator Infrabel.