Police investigate explosion at Swedish apartment building that injured 16

At least 16 people have been injured after a powerful explosion ripped through an apartment building in Sweden.

Hundreds more were evacuated after the blast, which occurred in the early hours of Tuesday in the Annedal district of Göteborg.

Sahlgrenska University Hospital spokeswoman Ingrid Frederiksson said 16 people were taken to the city's main hospital.

Six people — including three older women and a man in his 50s — were treated for serious injuries, police said. Four people remained in the hospital on Wednesday.

Police suspect that an explosive device may have caused the damage, and an investigation is underway.

Fires from the blast spread to several apartments in the complex, which burned for several hours before being extinguished.

Images from the scene showed thick white smoke billowing from the building's windows, while emergency crews swarmed the area.

"The rescue operation is ongoing and the cause of the detonation is not yet clear," a statement read.

"Investigative measures are being taken in the context of the preliminary investigation into a public nuisance."

"We believe something has exploded that is not of natural causes," Police spokesperson Thomas Fuxborg later told a news conference, adding that something had "probably" been placed at the site of the explosion.

According to AFP, the head of emergency operations stated that the building is not supplied with gas.

At a press conference, Swedish Prime Minister Stefan Löfven said the incident affects "the whole country".

"I think we all want to know more, want to understand what happened, what caused the explosion," added Interior Minister Mikael Damberg.

"The police have been able to start investigative work ... I think we should be careful not to contribute to speculation."

Sweden has been struggling for several years to deal with the rise of criminal gangs, which have included a high number of fatal shootings and explosions.