German police say four people have been injured in a knife attack at a gym in the western city of Duisburg.
Tuesday evening's attack occurred in Duisburg's old town and police asked residents to avoid the area.
Three people were in life-threatening condition, and one person was less severely injured, Duisburg police tweeted.
All four injured people are German citizens, police tweeted without giving any further details on their identities
“According to current information, one person has injured other people with an object" at a gym, they tweeted earlier.
Police said that a “stabbing or cutting weapon” was used in the attack, but did not give any further details.
The attacker appeared to still be on the loose, DPA reported.
“There has been no arrest,” police said, adding that a hunt was under way for the attacker. Investigators also said it was too early to talk about a possible motive behind the attack.
Several victims were taken to a hospital, while investigators searched the gym. Several witnesses to the attack, some still with their sports bags, were taken to a nearby restaurant so police could question them.
Helicopters were hovering above the gym and psychologists were brought in to help shocked witnesses.
Police said they received the first emergency calls at about 5.40pm local time.
Duisburg has about 500,000 residents and is at the junction of the Rhine and Ruhr rivers.
It used to be famous for its coal mining and steel production, but has in recent decades been plagued by high unemployment and poverty.
The President of the German Parliament, Baerbel Bas, who is from Duisburg, expressed shock over the attack.
“Terrible. My thoughts are with the injured,” Ms Bas tweeted. “I hope that the emergency services will soon be able to clear up the threatening situation.”
Last month, a gunman stormed a service at his former Jehovah’s Witness hall in the northern Germany city of Hamburg, killing six people before taking his own life after police arrived.
