Regional police chief Lars Wiren said officers sent to the adult education centre in Orebro, west of Stockholm, told reporters they were faced with "dead people, injured people, screams and smoke".

Anna Bergqvist, who is heading the investigation, said they were still working to pin down a motive for Tuesday's massacre, which has sent shockwaves across the Nordic country.

"What is the motive? ... We don't have an answer yet," she said.

Broadcaster TV4 published a video filmed by a student hiding in a bathroom in which shots can be heard outside and a person can be heard shouting: "You will leave Europe!"

Bergqvist told AFP that there were "multiple nationalities, different genders and different ages" among those who were killed.

The victims have not all been identified yet, according to police.

- Unused ammunition -

The Syrian embassy expressed "its condolences and sympathies to the families of the victims, among them Syrians," in a post on its Facebook page late on Wednesday.

Wiren told reporters that officers got the impression that "the shooting started being directed at police when they entered the school instead of students and staff".

Police found 10 empty magazines at the site and "a large amount of unused ammunition" next to the suspected gunman, who had turned the gun on himself and was dead when police reached him.

He has been identified by the Swedish press as 35-year-old Rickard Andersson, but there has been no official confirmation of his identity.

Swedish media reports painted a picture of the assailant as a local man who had been living as a recluse and was suffering from psychological problems.

According to Aftonbladet newspaper, he reportedly hid his weapons in a guitar case and changed into military style garb in a school bathroom, before opening fire.

Bergqvist told reporters that police believed they knew the identity of the assailant but said they would "not confirm such information" until they had verified the identity via DNA.

Police also said that several long-barrelled weapons had been recovered.

"He has a licence for four weapons, all of the four weapons have been seized. Three of those weapons were next to him" when police reached him, Bergqvist said.

The man had previously been enrolled at the school but had not attended classes there since 2021, Aftonbladet reported.

Health authorities said Wednesday that six people were being treated at Orebro's university hospital.

Three women and two men had undergone surgery for gunshot wounds and were in a "stable but serious" condition.

A woman was treated for minor injuries, Orebro County authorities said, adding that all the wounded were over the age of 18.

- 'Incomprehensible' -

Near the crime scene, people had put down notes among the tulips, roses, chrysanthemums and candles laid in memory of the students.

"There is also lots of love in the world. It can be easy to forget after a heinous act like this..." one note read.

Dressed in a black coat, 68-year-old retiree Margaretha came to place a candle on the frosty ground Thursday morning.

"It's incomprehensible, I'm not surprised but it's incomprehensible, especially since it happened very close to me, I live here," she said.

"There are so many shootings, explosions, it has become our daily reality now, unfortunately."

School attacks are rare in Sweden but shootings and bombings linked to gang violence have killed dozens of people each year.

In March 2022, an 18-year-old student stabbed two teachers to death at a secondary school in the southern city of Malmo.

Two months earlier, a 16-year-old wounded another student and a teacher with a knife at a school in the small town of Kristianstad.

In October 2015, three people were killed in a racially motivated attack at a school in the western town of Trollhattan by a sword-wielding assailant who was killed by police.