A man intentionally rammed a car into a crowd at a carnival procession in the German town of Volkmarsen, injuring dozens of people including children, police said.

The suspect, a 29-year-old German citizen, was arrested but could not be immediately questioned because he was injured in the incident and being treated by doctors.

He is being investigated on suspicion of attempted homicide.

Police spokesman Henning Hinn confirmed that Monday's crash was deliberate, adding: "There were several dozen injured, among them some seriously and sadly also children."

Volkmarsen, a town of about 7,000 people, is in Hesse, a central German state; all carnival parades across the state were cancelled as a precaution.

However, state police said they had no indication of a threat anywhere else in Germany.

Hesse Interior Minister Peter Beuth said of the roughly 30 people injured, about 10 were children.

"As far as I know, there are still no indications for the motive for the deed. This is also a subject of the investigations which are now being carried out with high pressure," said Beuth.

Seven victims were in serious condition, Frankfurt police chief Gerhard Bereswill told local media.

Forensic police officers are seen close to the site where a car drove into a carnival procession in Volkmarsen near Kassel, central Germany, on Rose Monday, February 24, 2020 [Uwe Zucchi/dpa/AFP]

The incident took place on the south side of Volkmarsen, outside a supermarket.

Video footage showed a silver Mercedes station wagon with local licence plates and its hazard lights blinking on the pavement while emergency crews walked by.

The carnival is popular in parts of Germany, especially in Rhineland cities such as Cologne and Duesseldorf, where festivities peaked on "Rose Monday" (February 24) with tens of thousands attending street parades featuring comical or satirical floats.

Monday's attack came less than a week after a far-right gunman killed at least nine people in a city called Hanau, which is also in Hesse - an assault which sent shock waves through Europe.