A bus fire in Kerzers killed at least six people and injured five others, prompting a criminal investigation.

Police in Fribourg Canton said the blaze may have been caused by a deliberate act, possibly involving someone pouring flammable liquid on themselves inside the bus.

The vehicle, operated by PostBus, was completely engulfed in flames when rescue teams arrived.

Swiss President Guy Parmelin expressed condolences to the victims’ families and said the circumstances are still being investigated, NBC News has reported.

Authorities said there is currently no evidence that the incident was a terrorist attack.