Two people have died and six others have been injured after a knife attack in a busy market square in Finland.

Police shot a suspect and are hunting possible other attackers after several people were stabbed in the city of Turku on Friday afternoon.

Authorities placed the city centre on lockdown and have reinforced security nationwide. They did not yet know if the attack was linked to terrorism.

"Nothing is yet known about the motives," said Finland's top police chief Seppo Kolehmainen.

Emergency services gathered following multiple stabbings in Turku's market square (EPA)

Witnesses reported seeing a man wielding a large knife and hearing gunshots and screams at the city centre's Puutori market square. Some said they saw a lifeless body lying on ground.

One of those stabbed was reported to be a woman pushing a buggy.

An attacker was taken into custody and was being treated in hospital after being shot in the thigh by armed officers.

Police urged people to keep clear of the city centre while officers searched for other perpetrators.

Police tend to an injured man inTurku (AFP/GettyImages) (AFP/Getty Images)

South-West Finland police tweeted at 4.40pm local time: "Several people stabbed in central Turku. People are requested to avoid the city centre."

They later added: "The police is searching for possible more perpetrators in Turku. People are asked to leave and avoid the centre of Turku.

Witnesses told of hearing screams of terror at the corner of the market square.

Laura Laine told Finnish broadcaster YLE: "We heard that a young woman was screaming. We saw a man on the square and a knife glittered. He was waving it in the air.

"I understood that he had stabbed someone."

Finland stabbings - locator map

Police warned people to be on alert at train stations and airports, while Turku's local government opened a crisis line for people in need of emergency help.

Officers were inspecting departing trains and buses, and carrying out patrols and additional surveillance.

Armed police were seen at Turku's harbour, where a helicopter circled overheard, and security has been heightened at Helsinki airport.

Interior Minister Paula Risikko she did not yet know whether the attack was related to terrorism.

Prime Minister Juha Sipila said the government was "closely following the events in Turku and ongoing police operation" and said ministers would meet on Friday.

Witnesses took to social media to tell people to avoid the city centre.

Jesse Brown said: "I saw the police shoot a man. There was some talk about a knife attack. People were running."

Video shared online appeared to show people running away from danger, reportedly shouting warnings in Finnish.

Turku is on Finland's south-west coast, about 85 miles west of the capital Helsinki.

Finland is traditionally peaceful but the Finnish Security Intelligence Service raised the terrorism threat level in June, saying it had become aware of more threats to the country.

The stabbings came a day after suspected Islamist militants ploughed into crowds in Barcelona, killing 13 people.