According to local media, the attacker is believed to have deliberately stabbed the victim in the neck.
German Chancellor Olaf Scholz said on Saturday that the perpetrators must be caught quickly and punished to the fullest extent of the law.
Interior Secretary Nancy Pager expressed her condolences and said security officials were “working diligently to catch the perpetrators and determine the circumstances surrounding the attack”.
Solingen is a city in North Rhine-Westphalia, famous for its steel industry, with a population of about 160,000. It is located about 15 miles (25 km) east of Düsseldorf and northeast of Cologne.
At a news conference early Saturday morning, the province's Home Secretary, Herbert Royle, said: “You don't want to believe what you see at the crime scene. It's a heavy burden. My heart goes out to the families of the victims and to the injured. We can only pray that those who were seriously injured survive.”
After the attack, which occurred around 10pm local time (9pm BST) on Friday, city authorities asked people to leave the Fronhof market area while police set up a cordon.
According to German news outlet Bild, emergency workers were seen at the scene treating the injured, and police later deployed 40 tactical vehicles to track down the stabbing suspect.
The vehicle is under the command of an SEK (Special Missions Unit) officer.
Roads were blocked and residents were told to stay indoors while police conducted searches.
Philipp Müller, one of the festival organisers, said on Friday that people were shocked but left the square peacefully after the attack.
Eyewitness Lars Breitzke told the Zollinger Tageblatt newspaper that he knew something was wrong when he saw a strange expression on one of the singers' faces on stage.
“And then one guy collapsed about a metre away from me,” he said.
