At least three people have died in the accident, the German police tell AFP. Initially, they stated that four people were dead, but later adjusted the figure downwards.
The accident occurred around 6:10 pm near the town of Riedlingen in the state of Baden-Württemberg, says a spokesperson for the police earlier on Sunday evening.
100 people are reported to have been on board the regional express train at the time of the derailment.
Images from the scene show train cars with extensive damage, one of which has overturned.
It is still unclear what caused the derailment, but according to the German Bild newspaper, a severe storm with heavy rainfall had recently hit the area where the accident occurred. The authorities are investigating whether a landslide caused by the water masses may be behind the accident, according to the newspaper.
Germany's Federal Chancellor Friedrich Merz says he is shocked by the incident.
"We mourn the victims. I extend my condolences to their families," he writes in a post on X.
The responsible railway company Deutsche Bahn also expresses its "deep dismay" and has set up a special hotline for those affected and their families.
