Police said a suspect had been arrested following the attack at a restaurant in the town of Rot am See at 12.45pm.
Some of the victims belong to the same family, spokesman Rudolf Biehlmaier told German broadcaster n-tv.
“According to my information, there were six dead and several injured,” he said.
“We are working on the assumption that this was a single attacker.”
The suspect is believed to be a German male but has not yet been identified by the authorities. Police said the suspect knew one or more of the victims.
A major operation involving the medical rescue services was launched near the train station in Bahnhofstrasse.
“Several injuries, probably dead in a building,” announced the local police force based in the city of Aalen, in the federal state of Baden-Württemberg.
“According to initial findings, there is a relationship [between the suspect and victims]. Currently no indication of further perpetrators.”
There was no suggestion of a terrorist motive and police asked the public to “refrain from speculation”.
It follows the recent high-profile shooting at a synagogue in Halle, central Germany, by a suspected neo-Nazi.
Rot am See, with a population of over 5,000, is located about 170km northwest of Munich.
Additional reporting by Associated Press