At least three people have been killed and four are seriously wounded, German police have said, after an attack at a festival in the city of Solingen in the country’s west.

An earlier report from German news agency dpa cited unidentified police sources as saying the weapon was believed to be a knife.

No one has been arrested and police were using vehicles and a helicopter to search for the assailant or the assailants.

The festival marking the city’s 650th anniversary and billed as a festival of diversity began on Friday and was supposed to run through Sunday.

The local Solinger Tageblatt newspaper reported that authorities called on people to leave downtown Solingen and that one of the festival organisers, Philipp Müller, said on a stage that emergency workers were fighting for the lives of nine people.

Rolling news channel NTV showed a video of Müller asking the crowd not to “panic” and to be careful leaving the premises because the attacker was still at large.

Witnesses said that people remained calm as they left the scene and media images showed that that the premises were empty apart from police and emergency vehicles.

Police declined to discuss a possible motive or the identity of the suspect.

Solingen has about 160,000 inhabitants and is located near the bigger cities of Cologne and Düsseldorf.

Mayor Tim-Oliver Kurzbach said the city was “in shock, horror and great sadness”.

“We all wanted to celebrate our city’s anniversary together and now we have to mourn the deaths and injuries.

“It breaks my heart that there was an attack on our city. I have tears in my eyes when I think of those we have lost. I pray for all those who are still fighting for their lives.

“I also have great sympathy with all the people who had to witness this; it must have been a terrible sight. I thank all the rescue and security forces for their efforts. I ask you, if you believe, to pray with me and if not, to hope with me.”

The attack occurred amid a heated political debate about rising knife violence in German cities.