Four people have been seriously hurt in an explosion and fire in a central residential area of the Swedish city of Gothenburg.

The immediate cause of the blast and blaze early on Tuesday was unclear.

At least 16 people were taken to hospital after firefighters pulled people out of a residential bloc from which smoke was billowing.

Three women and one man were treated for serious injuries, a Sahlgrenska University Hospital spokesman said.

Emergency services say they are working to evacuate people and put out fires following a building explosion in the Swedish city of Gothenburg. #Sweden https://t.co/zLhlXaZDlp pic.twitter.com/7SLnzeM5pO

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Swedish public services radio SR reported about 25 people had been taken to hospitals around Sweden’s second-largest city.

Police said they had opened an investigation but could not give more details.

Emergency services said they were working to evacuate people and put out fires in the building.

They ruled out a gas leak, but refrained from speculating on the cause of the explosion.

Anja Almen, who lives in the building, said she heard a commotion from the street just after 5am, about 15 minutes after the explosion.

“I went out on the balcony and I was shocked. There was smoke everywhere, from every stairwell,” she said by phone from a nearby church to which she and other tenants were evacuated.

“Fire trucks with ladders were pulling people from apartments.”

A spokesman for the emergency services said several hundred people had been evacuated from the vicinity of the explosion and fire.

The Nordic country has contended with surging gang crime in recent years, with rival groups employing explosives and fire arms to settle scores.

-Reuters