A man with a knife killed two people and wounded at least six in a stabbing rampage in a market square in the Finnish city of Turku on Friday, police said.
Police shot the suspected attacker in the leg and arrested him. They said they had yet to establish the identity of the man who appeared to be of foreign origin, or his motive.
They warned people to stay away from the city and reinforced security nationwide, with increased patrols and more surveillance, in case more people were involved. People were allowed to return to the city center a few hours later.
"At this stage, there is only one suspect and we are investigating whether there are more people involved... but it looks likely [he was alone]," said Markus Laine from the National Bureau of Investigation.
"At this stage, we do not investigate this [as a terror attack] but the possibility has not been ruled out," he told a news conference.
Interior Minister Paula Risikko said: "We have not been able to confirm the person's identity... we have been in contact with the immigration service as the person looks like a foreigner."
Eyewitnesses described the panic at the scene.
"A man walked towards the ice cream stand where I work, and he hit a woman three times. He started running, went past my kiosk, and he had a knife in his hand," Terttu Lehtinen told Reuters.
She said that some other men ran behind, apparently chasing him.
"We were sitting by the market square, just enjoying the afternoon. Suddenly people started screaming and yelling, they were hysterical," said another witness, who gave her name only as Reetta.
"We started running towards our car and, as we got there, my boyfriend said a woman had been stabbed several times in the neck," she told Reuters.
The six wounded were taken to hospital, police said.
Prime Minister Juha Sipila said: "My deepest condolences to the families and close-ones of the Turku victims. The events of the day are shocking us all." He added that the government would meet later.
Finland is usually peaceful but the Security Intelligence Service raised the terrorism threat level in June, saying it had become aware of terrorism-related plans in Finland.
The government has grown more concerned about attacks, partly since an Uzbek man killed four people in neighbouring Sweden in April by driving a hijacked truck into crowd in central Stockholm.
On Thursday, a suspected Islamist militant drove a van into crowds in Barcelona, Spain, killing 13 people and wounding scores of others.
European Commission President Jean-Claude Juncker said: "It is with great concern that I have learnt of the violent attacks in Turku, Finland. While details are still emerging, we strongly condemn this unprovoked attack which comes only 24 hours after the horror that unfolded in Spain."