PARIS >> A regional train hit a school bus on a crossing in southern France today, killing four children and critically injuring seven other people on the bus, the French interior ministry said. It was one of the worst rail accidents in France in years.

Photos from the scene tweeted by a local television station showed the train derailed and the bus shorn in half — with first responders gathered around.

It was not immediately clear why the accident happened. France’s SNCF national rail authority said witnesses described the crossing gates as functioning properly.

The school bus was carrying around 20 children aged between 11 and 15, the local authority said.

Nine other people on the bus and three on the train had less severe injuries.

It happened on a railway crossing in the small village of Millas, some 9 miles west of Perpignan, close to the border with Spain.

An SNCF official told The Associated Press that the train normally travels at 80 kilometers per hour at that location.

The official said “several witnesses said the barrier was down” at the time of the crash. She said 25 people were on the train at the time of the crash, and are “totally shocked.”

Transport Minister Elisabeth Borne and Education Minister Jean-Michel Blanquer were at the scene Thursday evening along with 70 firefighters, 10 emergency ambulances and four helicopters.

Blanquer tweeted “France is in mourning.”

Prime Minister Edouard Philippe was on an airplane en route.

French President Emmanuel Macron tweeted: “All my thoughts go to the victims of this terrible accident and their families. The government is fully mobilized to give them emergency help.”