Around 10 people have been killed in a shooting at an adult education centre, Swedish police said, the deadliest attack to take place in Sweden on what the prime minister said was a “painful day” for the country.

The gunman is believed to be among those killed and a search is continuing at the school for other possible victims, the local police chief told a press conference. The perpetrator’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 reporters.

Forest said police believed the gunman had acted alone and that they did not currently suspect terrorism as a motive, though he cautioned that much remained unknown.