OREBRO, Sweden -- Eleven people were killed in a shooting at an adult education centre on Tuesday, Swedish police said, marking the country's deadliest gun attack in what the prime minister called a "painful day."

Police said the gunman was believed to be among those killed and a search for other possible victims was continuing at the school, located in the city of Orebro. The gunman's motive was not immediately known.

"We know that 10 or so people have been killed here today. The reason that we can't be more exact currently is that the extent of the incident is so large," local police chief Roberto Eid Forest told a news conference.

Later in the evening the police website said: "At this time, there are 11 deaths due to the incident. The number of injured is still unclear. We currently have no information on the condition of those who have been injured."

Forest told the press conference police believed the gunman had acted alone and that terrorism was not currently suspected as a motive, though he cautioned that much remained unknown. He said the suspected gunman had not previously been known to police.

"We have a big crime scene, we have to complete the searches we are conducting in the school. There are a number of investigative steps we are taking: a profile of the perpetrator, witness interviews," Forest said.

The shooting took place in Orebro, some 200 km (125 miles) west of Stockholm, at the Risbergska school for adults who did not complete their formal education or failed to get the grades to continue to higher education. It is located on a campus that also houses schools for children.

Ali Elmokad was outside the Orebro University Hospital, looking for his relative, not yet knowing if he was among the injured or the dead.

"We've been trying to get hold of him all day, we haven't been successful," he said, adding that he had a friend who also attended the school. "What she saw was so terrible. She only saw people lying on the floor, injured and blood everywhere."

Police said it was still going through the crime scene and had searched several addresses in Orebro after the attack.

Late on Tuesday, police vans and personnel were still outside an apartment building in central Orebro that had been raided earlier.

"We saw a lot of police with drawn weapons," said Lingam Tuohmaki, 42, who lives in the same building. "We were at home and heard a commotion outside."

Prime Minister Ulf Kristersson said it was the worst mass shooting in Swedish history.

"It is hard to take in the full extent of what has happened today -- the darkness that now lowers itself across Sweden tonight," he told a news conference.

King Carl XVI Gustav conveyed his condolences. "It is with deep sadness and dismay that my family and I received the news about the terrible atrocity in Orebro," he said.

European Commission President Ursula von der Leyen expressed her sympathy on X, saying: "In this dark hour, we stand with the people of Sweden."

'We Started Running'

Maria Pegado, 54, a teacher at the school, said someone threw open the door to her classroom just after lunch break and shouted to everyone to get out.

"I took all my 15 students out into the hallway and we started running," she told Reuters by phone. "Then I heard two shots but we made it out. We were close to the school entrance.

"I saw people dragging injured out, first one, then another. I realised it was very serious," she said.

Many students in Sweden's adult school system are immigrants seeking to improve basic education and gain degrees to help them find jobs in the Nordic country while also learning Swedish.

Sweden has been struggling with a wave of shootings and bombings caused by an endemic gang crime problem that has seen the country of 10 million people record by far the highest per capita rate of gun violence in the EU in recent years.

However, fatal attacks at schools are rare.

Ten people were killed in seven incidents of deadly violence at schools between 2010 and 2022, according to the Swedish National Council for Crime Prevention.

Sweden has a high level of gun ownership by European standards, mainly linked to hunting, though it is much lower than in the United States, while the gang crime wave has highlighted the high incidence of illegal weapons.

In one of the highest-profile crimes of the past decade, a 21-year-old masked assailant driven by racist motives killed a teaching assistant and a boy and wounded two others in 2015.

In 2017, a man driving a truck mowed down shoppers on a busy street in central Stockholm before crashing into a department store. Five people died in that attack.