Two children were among four people killed when a school minibus was hit by a train after appearing to plow through a barrier at a level crossing in northern Belgium on Tuesday morning, police said.

Local authorities in Buggenhout in northern Belgium said in a statement that a “serious traffic accident” took place in the town at around 8 a.m. local time on Tuesday. Photo s from the scene showed a minibus laying on its side next to a railway track.

When asked if the incident was due to human error, police spokesperson An Berger said “it’s too early to say anything.”

The fatalities included two pupils aged 12 and 15, as well as an attendant, 27, and the bus driver, 49, according to Public Prosecution Service spokesperson Lisa De Wilde.

Five more children were seriously injured during the incident and are now in stable condition in hospital, De Wilde said.

An investigation has been opened into the cause of the accident, with a traffic expert appointed and a forensic laboratory active on the scene, the local government said in a statement.

While the inquiry is still in its early stages, it has been confirmed that the barriers at the level crossing were closed and the red warning signal was operating at the time of the collision.

Belgian Justice Minister Annelies Verlinden said on X that the accident involved a school bus, with local media reporting the vehicle was transporting students from a nearby special education school.

“Words fail at the accident in Buggenhout, in which a train and a school bus were involved,” she said.

Ursula von der Leyen, President of the European Commission, said she was “heartbroken” to learn of the accident. “My deepest condolences go out to the victims’ families and their loved ones,” she said on X. (CNN)