BERLIN, July 21 (Xinhua) -- Four people were killed in a massive 10-car pile-up in south-western Germany on Saturday, German news agency DPA reported.

The crash occurred on a motorway near the city of Heilbronn and left a "huge debris field", a police spokesman said.

The cause of the accident had not yet been determined, DPA reported.

In addition to a number of people who were treated at the site with minor wounds, four people were seriously injured.

About 100 first responders arrived at the scene and four helicopters were involved in the operation, it said.