German police say four people have been injured in a stabbing attack at a commuter rail and subway station in downtown Frankfurt.

Frankfurt police spokeswoman Chantal Ench said the attack took place on Saturday afternoon inside the Hauptwache station.

Ench says four people were taken to the hospital with stab wounds, but she didn't have details beyond that.

The knifeman was reported to still be on the run.

She says police are investigating to find out how many people were involved. She also didn't have any details on the ages and genders of the injured.

According to Hessenschau, a local news outlet, one person was seriously hurt in the incident while the three others sustained light injuries.

It said the incident, which involved youths aged between 16 and 18 erupted at about 17.40 local time.

Blood stains were seen on the concourse of the station.

The motive for the attack remained unclear. Police in Frankfurt urged the public to avoid fear mongering.

"We are asking to refrain from speculation... You are scaring your fellow citizens. There is no danger," Frankfurt police said on their official Twitter account.