Police say a deadly bus fire in Kerzers was likely intentional, but currently shows no signs of terrorism, as investigations continue into the tragedy that killed six.

KERZERS: A bus fire that killed at least six people in western Switzerland was likely ignited deliberately but is not currently being treated as a terror attack, police said.

The blaze broke out on the main street of the small town of Kerzers, around 20 kilometres west of Bern, on Tuesday evening.

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

Fribourg Canton police communications chief Martial Pugin confirmed an intentional act is the most likely scenario.

He stated there is presently no evidence to suggest it was a terror attack.

Police spokesman Frederic Papaux said the fire left at least six dead and five injured, three of them seriously.

He also indicated evidence pointed to the fire being deliberate but would not speculate on whether it was a suicide.

Authorities were unable to confirm how many passengers were aboard at the time of the blaze.

Several ambulances and a helicopter were sent to the scene, with investigators working late into the night.

Three injured people were taken to hospital, with two in a grave state and the third able to return home overnight.

Two other people were examined on site but did not need hospital treatment.

By early Wednesday, the charred husk of the bus was removed from the roadway.

A hotline has been opened for witnesses as authorities try to determine the exact circumstances.

A press conference is scheduled at the cantonal police headquarters near Fribourg.

Fribourg police said a criminal investigation had been opened by public prosecutors.

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

A bar fire in the ski resort of Crans-Montana on New Year’s Day killed 41 people and injured 115.

Swiss President Guy Parmelin said he was shocked and saddened that people had once again lost their lives in a serious fire.

The bus involved was a PostBus, a distinctive yellow service that is a feature of Swiss rural life.

PostBus and Swiss Post CEO Stefan Regli said all employees were shocked by the terrible tragedy.

 The Sun Malaysia