The attacker entered the theatre in the Neuenheimer Feld area, opened fire and then fled the scene, according to Mannheim Police.

He is now dead after turning the gun on himself.

Some are seriously wounded, according to police.

"There is no further danger, but we continue to search the area," said Patrick Knapp, a spokesperson for Mannheim Police.

Bild quoted news agency dpa as saying the attacker was a student.

Police said his motive is still unclear, but investigators reportedly told Bild that he appears to have had no political or religious motivations.

He used a long-barreled firearm during the attack, and Bild reported that he may have been carrying several rifles.

Officers had earlier asked the public to avoid the area, where Heidelberg University's natural science faculties are located, along with parts of the university hospital.

The crime scene at Neuenheimer Feld was cordoned off, with a large deployment of police and emergency services on the scene.

Federal agriculture minister Cem Özdemir, who is from the larger Baden-Württemberg area, said the news was "shattering", adding: "My thoughts are with the injured, with the university staff, with police and all other emergency services."

Located south of Frankfurt, Heidelberg has about 160,000 residents.

The university's press office declined to give any details about the shooting and said all inquiries should be directed to police.