At least six people died and three others were injured in a bus fire on Tuesday in a small town in western Switzerland, in what police said may have been a deliberate act following reports that a person on board set fire to themselves.

Police said the bus became engulfed in flames on a road in Kerzers, a town in the canton of Fribourg, about 20 km (12 miles) from the Swiss capital, Bern.

"At this stage, we have elements suggesting a deliberate act by a person who was inside the bus," said Frederic Papaux, a spokesperson for Fribourg police.

Investigators were looking into reports that a person had poured fuel on themselves, said Christa Bielmann, another local police spokesperson. It was too early to say whether the incident was terror-related, she told a press conference.

Three injured people were taken to hospital, police said. Two other people caught up in the blaze also received attention but did not need to be hospitalized.

Passengers were seen escaping from the burning bus, panicked and injured, Papaux said, adding that no other vehicle was involved.

Swiss media outlet 20 Minutes said it had seen a video taken at the scene in which an injured person said: "A man set himself on fire. He poured gasoline over himself and then lit himself."

Video after the flames were extinguished showed the charred remains of the vehicle, a yellow so-called Postauto.

Swiss President Guy Parmelin offered his condolences and said the incident was being investigated.

"It shocks and saddens me that once again people have lost their lives in a serious fire in Switzerland," he said in a statement on X, noting investigations were under way. In January, Switzerland was rocked by a fire in a bar in the Swiss ski resort of Crans Montana that killed 41 people and injured 115.