Fire has gutted a commercial passenger bus in the north Queensland city of Townsville.

The bus was parked on The Strand when it burst into flames shortly after 3:00pm (AEST).

Authorities said no passengers were on board at the time and the driver escaped injury.

Senior Sergeant Darren Randall said the driver was caught by surprise as the fire rapidly spread.

"Look, I've had a talk to the bus driver - he is, as you can imagine, fairly shaken but thankful he had the ability to get off the bus in time before the fire fully engulfed it," he said.

"[He is] thankful that there were no passengers on the bus, and he's being well cared for at the moment by representatives from Sunbus."

Witnesses said fire engulfed the bus within minutes.

"Like a big explosion happened and everything," one man said.

"When it blew up, it just went straight through my body, it felt so weird," another witness said.