Investigators worked through the wreckage of a high speed train crash in eastern Belgium on Monday that killed at least three people and injured nine others, AFP reports.

A fast-moving passenger train late Sunday slammed violently into the back of a slow-moving freight train that was travelling on the same track for reasons that remain unexplained.

Authorities said lightning and flood damage caused by heavy storms that affected all of western Europe in the past few days were being explored as a possible cause. Investigators were on the scene, but a spokeswoman for the prosecutor’s office in Liege warned that finding the cause “would be difficult”.