Three people have been killed in a shooting in the Swedish city of Uppsala, police have confirmed.

The shooting took place at a hair salon close to Vaksala Square in the centre of the city, local media reported. The shooter, who fled on a scooter, is still on the run, according to the reports.

Officers have cordoned off a large area and a murder investigation is under way.

The incident happened on the eve of the Walpurgis spring festival, which brings large crowds onto the streets of Uppsala, a city located north of the capital Stockholm, and known for its university.

"Everything happened so fast. It just went bang, bang, bang," a witness told Swedish channel TV4.

Another man said he was cooking at home when he heard "two bangs that sounded a bit like fireworks" going off outside on the street.

He told Swedish television he was "very surprised and scared" and shortly after "swarms of police and ambulances" started blocking off the street and telling people to move back.

A major effort is under way to find the shooter, with a police helicopter joining in the search, police spokesman Magnus Jansson Klarin told TV4.

Train services had been stopped in the area to stop the perpetrator using them to get away, Mr Klarin said, but they have now resumed.

Police officers have been going door-to-door to seek further witness information.

Meanwhile Justice Minister Gunnar Strömmer described the incident to TV4 as a "brutal act of violence".

In an update on their website, Swedish police acknowledged "concern among the public" ahead of the upcoming Walpurgis celebrations, but their initial assessment is that this was an "isolated incident" and there is "no danger to the public".

The identity of the victims and the shooter are still unclear. But there has been increasing concern over the number of shootings and gang attacks in recent years in Sweden, and the government has said it wants to tighten the country's gun laws.

In February, 10 people were killed in a shooting at an adult education centre in the Swedish town of Orebro. (BBC)