European Union (EU) leaders have sent their condolences to families of the victims of Monday's train collision near Brussels, which killed at least 18 people and injured more than 150.

European Council President Herman Van Rompuy, a former Belgian prime minister, expressed shock and sorrow on Monday at the crash in the Belgium town of Halle, some 15 km southwest of Brussels, one of the worst rail accidents in Belgian history.

European Commission President Jose Manuel Barroso expressed his "deep sadness", saying the EU executive stood ready to help where possible.

"It is with profound shock that I've learned of the terrible train crash in Halle this morning. My thoughts and those of the European Commission are with the families of those affected by this tragedy," he said in a statement on Monday.

His remarks were echoed by head of the European Parliament, Jerzy Buzek, who also provided his "sincere sympathies and condolences" to the families of the victims.

French President Nicolas Sarkozy also relayed his condolences and support to the victims and to the people of Belgium.

He said in a letter to King Albert II of Belgium that "I want to send you, on behalf of the people of France, as well as on mine, my sincere condolences and support between our two countries during this event."

"I want to express to the victims' families as well as the injured people my sympathy during these dramatic circumstances," he said.

The train crash occurred at 8:45 a.m. local time (0745 GMT) on Monday morning. The cause of the collision is still under investigation, with suspicion of a mistake by one of the drivers as well as a lack of safety equipment.

Belgian Prime Minister Yves Leterme cancelled his visit to the Balkans on Monday and rushed to the same afternoon. Shortly after the crash, King Albert II interrupted his vacation in southern France and returned home immediately.