Swedish authorities say a powerful explosion outside a police station in southern Sweden has caused significant damage to the building.

There have been no injuries and nobody has been arrested.

Police haven't said what caused the blast at the police station in Helsingborg.

The country's top police official, Dan Eliasson, called it "an attack against society."

Police forensics work at the scene (EPA)

The explosion caused considerable damage to the police station's entrance and shattered dozens of windows in nearby buildings.

No one has claimed responsibility for the blast about 50 kilometres (30 miles) north of Malmo, Sweden's third largest city.

Suburban feuds between criminal gangs fighting over territory have taken place in major Swedish cities in recent years.

The explosion wasn't immediately being investigated as terrorism.

A police officer stands guard outside the roped off area surrounding the police station in Helsingbor (EPA)

"It is fair to believe that this is a consequence of the good police work we do," police spokesman Patric Heimbrand told a news conference.

"We work in heavy criminal environments and some of them could be irritated. But to those I'd say that we cannot be influenced."

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Regional police chief Carina Persson told a news conference that Swedish Prime Minister Stefan Lofven had been informed of the blast as is customary after such incidents, but she didn't elaborate.

She declined to comment on whether there could any links to a similar blast on 30 November, 2014, against a police station in Malmo which hasn't been solved.

Mr Lofven told Sweden's TT news agency the blast was "extremely serious" and it was "an attack on our democracy".

"Violence against police must never be accepted," he was quoted as saying, adding that the fight against serious crime must be intensified "with stricter laws, better tools and increased resources to the police".