Children among the dead after train and school bus collide in France

Four children are dead and seven other people are critically injured after a regional train smashed into a bus at a crossing in southern France overnight.

In one of the worst rail accidents in France for years, local media is reporting that at least 20 passengers were injured following the incident near Perpignan.

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

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

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

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

The crash happened in the small village of Millas, which is about 15 kilometers west of Perpignan, close to the border with Spain.

A passenger from the train, named Barbara, said "it was a very violent crash - it seemed as if the train would derail".

An SNCF official told The Associated Press that the train normally travelled at 80km/h 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 were "totally shocked."

Transport Minister Elisabeth Borne and Education Minister Jean-Michel Blanquer were at the scene after the crash along with 70 firefighters, 10 emergency ambulances and four helicopters. Blanquer tweeted "France is in mourning."

Prime Minister Edouard Philippe is flying to the site of the crash, with President Emmanuel Macron tweeting "all my thoughts go to the victims of this terrible accident and their families. The government is fully mobilized to give them emergency help."