Swedish police are investigating whether an explosive device may have been planted at an apartment block in Gothenburg following a huge blast which caused serious injuries to residents.
Emergency responders said that the blast did not look like an accident, in a country that has suffered dozens of actual or attempted bombings linked to violent criminal gangs in recent years.
"It's obvious that a crime cannot be excluded," Interior Minister Mikael Damberg told a joint press conference with Prime Minister Stefan Lofven.
The powerful explosion ripped through the building in the Annedal district shortly before 5am on Tuesday, sending panicked residents fleeing.
Sixteen people were hospitalised, including four with serious injuries, according to a spokeswoman for Sahlgrenska University Hospital.
They include three women aged between 60 and 80, as well as a man in his 50s. Earlier reports suggested 25 had been injured.
Police told Swedish broadcaster TV4 that investigators think foul play may have been involved. They suspect someone placed a device in or just outside the multi-storey building.
Officers are looking into whether any tenants were being targeted.
“We suspect that someone might have placed something that has exploded,” said police spokesman Thomas Fuxborg.
“That is the word we got when the alarm was given.”
Earlier, Mr Fuxborg said officers believed the explosion was unlikely to be due to "natural causes".
According to regional newspaper Goteborgs Posten, a police officer who recently testified in a major gang trial in Sweden's second city lives in the building.
Asked if the person could have been the intended target, a police officer, whose name was not disclosed, told the newspaper: "Obviously we will look into this."
Other media reports suggested that multiple witnesses had been staying in the building.
Sweden’s national bomb squad were called in to carry out an investigation.
Sweden’s Prime Minister Stefan Löfven and Minister of the Interior Mikael Damberg held a press conference on Tuesday afternoon to discuss the grim events.
Mr Damberg was questioned by a reporter on whether the explosion may have been a deliberate act targeted at a police officer. The journalist also referenced the fatal shooting of an on-duty police officer in July.
“I do not want to precede the police investigation," said Mr Damberg in comments carried by Swedish newspaper Aftonbladet.
“After the terrible police murder, the police region has had a major offensive and the summer has been calm.
“They have the resources required, but I am sure that the rest of Police Sweden are prepared to assist if required.”
Mr Löfven expressed his sympathy towards the injured and all residents of the building. He also thanked the police and rescue services for their efforts.
More than 100 residents have been transferred from the block of apartments.
Emergency services said they put out fires and were working to rescue people trapped inside the building.
Fifty firefighters attended.
Jon Pile, operations manager at the greater Gothenburg rescue service, said: “It was burning in several places in the property and in several apartments, after the explosion.”
One fireman was reportedly injured while trying to put out the flames and has been taken to hospital.
"Several apartments and stairwells are affected. It is at present unclear what has caused the explosion," the emergency services for the wider Gothenburg area said.
Some people were said to have used sheets tied together to lower themselves down to the ground from windows.
A 24-year-old man who lives in the apartment block said he was woken up by a huge bang.
Theodor Oreus told Swedish daily newspaper Aftonbladet that his front door was slammed shut by the pressure wave and smoke was billowing out of the apartment.
“When we came down to the courtyard, people were fainting on the ground,” he said.
Lars-Gunnar Wolmesjö, another resident who managed to escape the building unscathed, said he was awoken by a noise that “sounded like something fell down on the floor above me”.
He rushed to his balcony where he spoke to his upstairs neighbour who handed his young son down to him.
Pastor Daniel Dalemo of Saron Church, close to the affected building, said he had welcomed 50 people to the place of worship to offer help and support.
City authorities are also assisting people at various locations. One worker said people had arrived wearing bathrobes after they fled the burning building.
Anja Almen, who lives in the building, said she heard a commotion from the street just after 5am.
Speaking by phone from a church nearby the burning building, she said: "I went out on the balcony and I was shocked."
"There was smoke everywhere, from every stairwell," she added. "Fire trucks with ladders were pulling people from apartments."
The Nordic country has contended with surging gang crime in recent years, with rival groups employing explosives and firearms to settle scores.
Gothenburg, a major city in the west coast of Sweden, has a population of 580,000.
Police said they had opened an investigation.