AN INFERNO ON a Swiss bus that killed six people was seemingly started by a “disturbed” man on board who set himself alight, the investigating prosecutor said Wednesday.

The blaze happened on Tuesday evening in the small town of Kerzers, around 20 kilometres west of the capital Bern.

Videos shared on social media showed flames several metres high bursting out of the windows, and black smoke rising into the sky.

The suspect “got on with his two bags and at some point stood up, doused himself with petrol, and set himself on fire”, Fribourg canton’s public prosecutor Raphael Bourquin told reporters.

The man “is someone in their sixties, but who seems to be quite marginalised, someone potentially psychologically disturbed, who is known to the medical community and who has apparently had some problems recently”, he said.

“There is absolutely no evidence to suggest that this could be a terrorist act,” Bourquin said, adding that “it appears that this person is among the deceased”.

The man, who lived in the neighbouring Bern canton, had recently been in hospital with a physical ailment but had been missing for a day or two, with his family notifying the police of his disappearance, said the prosecutor.

‘Astonishing’

Besides those killed, five people were injured in the fire. Three people were taken to hospital; two are in a serious condition and the other has since returned home.

Two other people were treated at the scene by emergency responders.

Fribourg police chief Philippe Allain said detectives were trying to work out who got on and off the bus along its route from the nearby town of Dudingen, to pinpoint how many people were on board at the time.

The potential victims were born between 1961 and 2009, he said. Autopsies have been ordered and the police are not yet confirming the identities of the deceased.

Allain said witnesses reported some people escaping from the bus who were “engulfed in flames”.

“The speed at which the fire spread was quite astonishing,” he told AFP.

That the suspect set himself on fire is the “leading hypothesis, based on witness statements, initial video analysis, and the sequence of events”, he said.

“We’re now going to work on profiling the suspected perpetrator and determine his motives by analysing what we can find at his home and on his mobile phone.”

‘Extremely sad times’

Before dawn on Wednesday, the charred shell of the bus had been removed, leaving a few traces of melted tar on the road and a faint smell of burning in the air.

The bushes and street signs beside the road were scorched.

During the day, several people came to lay bouquets of flowers at the scene of the tragedy.

It is the second major multiple-casualty fire in Switzerland in less than three months.

In the early hours of January 1, a bar in the ski resort of Crans-Montana caught fire as people celebrated the New Year. A total of 41 people died, with another 115 injured.

Swiss President Guy Parmelin visited the scene in Kerzers on Wednesday and laid flowers during a ceremony.

Around 300 people were present, including emergency service workers called into action the night before.

“Once again, we are going through extremely sad times,” Parmelin said.

“It is in moments like these that the words solidarity and humanity take on their full meaning.”

The bus involved was a PostBus – a feature of Swiss rural life.

The distinctive yellow buses serve more remote areas, connecting them with towns, while also carrying letters and parcels.

They are used by around half a million people every day, notably schoolchildren.