(CNN)Sixteen people have been injured -- including four critically -- after an explosion led to a large fire in an apartment building in the Swedish city of Gothenburg, emergency services told CNN Monday.
Explosion and fire with 'no natural explanation' injures 16 in Sweden, as police hunt for clues
The blast happened at 4:45 a.m. local time, according to Swedish police who are investigating the cause of the explosion.
"The fire department has confirmed that there is no gas in that building, so we have ruled out a gas leak for the moment," said Stefan Gustafsson, a spokesman for Sweden's western regional police.
"There is no natural explanation for the explosion," Gustafsson said.
In total, 16 people have been sent to hospital, with the possibility that "more people will be brought in, we don't know yet," a press officer at the Sahlgrenska University Hospital in Gothenburg told CNN.
The fire has been brought under control and crime technicians are now surveying the scene for evidence, Swedish police told CNN.
Police spokesperson Thomas Fuxborg, who is at the site of incident, told reporters that something had "probably" been placed in the apartment complex.
In recent years, gang violence has been on the rise in Sweden, with both homemade explosive devices and guns being previously used by rival gangs to settle disputes.
Swedish Prime Minister Stefan Lofven said it was too early to say exactly what had happened in Gothenburg but the whole of Swedish society would respond if criminals were behind the explosion.
"As a society we will do everything possible to fight gang crime," he told a news conference. "People should be able to feel safe."
Sweden has one of the highest rates of gun homicide in Europe due to the steady increase of violent activities by organized gangs. In 2019, 257 attacks involving explosives were reported in the Nordic country, according to data from the Swedish national council for crime prevention.
The Swedish daily newspaper, Aftonbladet, reported that one of the residents in the apartment block where the explosion took place was involved in a witness protection program, but police officers CNN spoke to would not comment on the claim.
"We can say nothing about who was living in the building while the investigation is ongoing, it is against the law," Gustafsson said.