In a powerful explosion followed by fire, numerous people were injured in the Swedish city of Gothenburg, several of them seriously.

According to the police, the detonation occurred early Tuesday morning in an apartment building in the Annedal district.

Afterwards, fires broke out in the apartment block, residents occasionally escaped through windows and balconies outside, as the broadcasting station SVT reported.

For hours afterwards, smoke continued to pour out from inside the building.

The background to the explosion initially remained unclear.

"We believe that something has exploded, which is not a natural consequence," said police spokesman Thomas Fuxborg in the morning on site.

It is probably something that has been placed in the place, but this has to be seen first.

The police opened preliminary investigations into general destruction.

There were initially no suspects.

Different information was available on the number of injuries.

Fuxborg spoke of around 20 people who had come to the hospital, the rescue workers on site of 6 seriously injured.

According to the TT news agency, at least 16 people were taken to Sahlgrenska University Hospital.

Four of them were seriously injured, including three women and one man, all of whom are then over 50 years old.

In Sweden there have been deliberately caused detonations again and again in recent years, the background of which lies in the criminal gang milieu.

Larger cities such as Stockholm, Gothenburg and Malmö are particularly affected, but in isolated cases also smaller towns.

Usually, however, people are rarely injured.

SVT initially reported, citing the head of operations, that the explosion had occurred in the courtyard of the apartment building.

As a result, fires started in several staircases.

Hundreds of people were therefore brought to safety.

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