A manhunt is under way after three people were killed and eight others injured in a knife attack in the western German city of Solingen, police say.

The attack happened during a festival in the city centre on Friday evening. Five of those injured are in a critical condition, according to German media reports.

On Saturday, police said they are still looking for the attacker, with national security forces deployed to the scene. They gave no details of a motive.

The man reportedly stabbed passers-by at random when the industrial city was celebrating 650 years since it was founded.

The attacker is believed to have deliberately stabbed his victims in the neck, local media report.

Germany’s Chancellor Olaf Scholz said on Saturday that the assailant must be caught quickly and punished to fullest extent of the law.

Interior minister Nancy Faeser expressed her condolences, saying security authorities are “doing everything they can to catch the perpetrator and determine the background of the attack”.

Solingen – a city in North Rhineland-Westphalia famous for its steel industry – has about 160,000 inhabitants. It lies about 15 miles (25 km) east of Düsseldorf and north-east of Cologne.

In a news conference in the early hours of Saturday, regional interior minister Herbert Reul said: “You don’t want to believe what you see here at the crime scene. It weighs heavily. My thoughts are with the relatives of the victims and the injured. We can only pray that the seriously injured will survive.”

The city’s authorities asked people to leave the Fronhof market area after the attack at about 22:00 local time (21:00 BST) on Friday, as police set up security cordons.

Emergency crews at the scene were seen treating the injured and police later deployed 40 tactical vehicles in the hunt for the stabbing suspect, according to German news outlet Bild.

The vehicles are being commanded by SEK (Special Task Force) officers.

Roads have been blocked and residents told to stay indoors as officers carry out their search.

Speaking on Friday, Philipp Müller, one of the festival organisers, said people were shocked but left the square peacefully after the attack.

Eyewitness Lars Breitzke told the Solinger Tageblatt newspaper that he knew something was wrong when he saw a singer on stage with a strange expression on their face.

“And then a person fell over just a metre away from me,” he said.

Police spokesman Alexander Kresta was quoted by German media as saying “we are currently assuming that it was one person” after talking to numerous eyewitnesses.

Police also said they “have no indication of his whereabouts”, nor details about his appearance.

In a Facebook statement, Solingen Mayor Tim Kurzbach said: “Tonight all of us in Solingen are in shock, horror and great sadness. We all wanted to celebrate our city anniversary together and now we have to mourn the dead and injured.

“It breaks my heart that an attack has happened in our city. I have tears in my eyes when I think of those we’ve lost. I pray for all those still fighting for their lives. Also my greatest sympathy for all those who had to experience this, these images must have been horrific.”

Speaking to the BBC later on Friday, Solinger Tageblatt’s deputy editor Björn Boch said the celebrations had been “supposed to last for three days, and the city expected 25,000 people every night.

“The city was just packed with people,” he said, estimating that “a few thousand people” were at Friday’s free event.