Finnish police say they are investigating a knife attack that left two people dead in the western city of Turku as a "terrorist killing".

Security forces shot and wounded the knife-wielding suspect on Friday, arresting him minutes after a stabbing spree at a market square in Turku.

"The act had been investigated as murder, but during the night we received additional information which indicates that the criminal offences are now terrorist killings," an official statement said on Saturday.

The suspect was identified as an 18-year-old Moroccan citizen, but police did not release his name.

He is being treated in hospital in intensive care for a gunshot wound to the thigh.

The National Bureau of Investigation, which is heading the probe, said those killed in the attack were Finnish citizens, while the wounded include one Italian national and two Swedes.

A total of eight people were wounded, the police said.

READ MORE: Timeline - Deadly attacks in Europe

Alexis Kouros, the editor-in-chief of Helsinki Times, told Al Jazeera that such attacks were rare in Finland.

However, the Finnish public had been expecting one because of a rise in deadly attacks in other European cities in recent years, he said.

"People are calm. There is not much speculation," he said. "Somehow, this was expected because it has happened everywhere."

There were questions about the attacker's motives, Kouros said, noting that Finland has not been involved in military actions or wars in other countries.

However, some Finnish immigrants have left the country to fight in the Middle East with the Islamic State of Iraq and Levant (ISIL, known as ISIS) group, he added.

In a separate development, officials raided a flat in Turku overnight on Friday and arrested five others.

"We are investigating the role of these five other people, but we are not sure yet if they had anything to do with (the attack)," Markus Laine, a police superintendent, told the AFP news agency on Saturday.

"We will interrogate them, after that we can tell you more. But they had been in contact with the main suspect."

Officials said it was likely the suspect acted alone, but added they were looking for "other possible perpetrators".

Finland raised its emergency readiness across the country after the stabbing, increasing security at airports and train stations and putting more officers on the streets.

In June, Finland's intelligence and security agency Supo raised the country's terror threat level by a notch, from low to elevated, the second notch on a four-tier scale.

It said at the time that it saw an increased risk of an attack by the ISIL group.