A witness has described "pandemonium" in a small north Queensland town after a ute crashed into a cafe, igniting a gas explosion and hospitalising 20 people, five of whom had serious injuries.

The ute ploughed into the rear of the Serves You Right Cafe on Grigg Street, Ravenshoe, hitting gas bottles which ignited the huge explosion.

Tablelands fire inspector Greg Livingstone said the diners, two of whom were firefighters, had varying degrees of burns and respiratory injuries.

Sorry, this video has expired Cafe blast leaves 20 people injured in far north Queensland. ( Kirsty Nancarrow )

"There was fire damage throughout, windows blown out, and fairly severe structural damage to the rear of the premises," he said.

Patients were triaged in the street, some wrapped in blankets, others laying on stretchers.

The three critically injured were flown to the Cairns and Townsville hospitals.

Allan Buckman and Deearn Fallow were inside the cafe at midday when they heard a small bang.

Mr Buckman said he looked around and saw what appeared to be gas filing the restaurant.

"I looked at my girlfriend and I just said 'run'," Mr Buckman said.

Locals tried to help in the aftermath of the explosion. ( Channel 7 News )

"Within three seconds - with me and her running and falling out the door - the place went 'boom'.

"We could feel the heat and the fire."

The couple were thrown to the ground and quickly scrambled to their feet to keep on running.

"It was pretty freaky," Mr Buckman said.

"It's a horrible scene to see people that way and you can't take it away."

Emergency services were called to the Serves You Right Cafe about 12:00pm. ( Channel 7 News )

Kiaya-lee Fowle was in her car 30 metres away from the cafe.

She said the ute had clipped a tree and was out of control.

"It clipped a little tree up there and then it ran into the back of the shop," she said.

"To begin with, I thought it was a stolen car coming up over the grass then when it went past there was just no control in that car at all."

"The ute wanted to keep going, it was just spinning on the spot.

"It just exploded, the side roof lifted."

Firefighters have extinguished the blaze at the cafe. ( Channel 7 News )

Ms Fowle said the flames started coming towards her car, and then she heard heaps of people screaming.

"I walked around the front of the shop and I seen a couple of people there with all their clothes burnt, like stuck to them," she said.

"Some had very horrific facial burns."

Ken Hodge said a local had told him the ute collided with another car and became airborne to crash into the gas bottle.

Police are yet to confirm how or why the ute had left the street.

A crime scene has been established.

When Mr Hodge arrived, he saw the car still alight and the cafe blackened inside.

"Basically it was pandemonium in the middle of Ravenshoe," he said.

Locals help treat some of the injured. ( Supplied: Darrin Leonard )

"A lot of people running back and forth from one side of the street to the other, trying to get assistance.

"It was a lot of local people coming out of their businesses to assist.

"You could obviously see there were very upset people."

Kate Lewis, who works in a supermarket opposite the cafe, said it was an horrific scene.

"We just heard a massive sonic boom and went running out and saw the cafe on fire and lots of burnt people," she said.

"And everybody's just over there helping and it's an absolutely horrific scene."

Police are investigating the incident which injured more than 20 people. ( Supplied: Queensland Ambulance Service )

Ravenshoe is a farming community on the Tablelands with a population of less than 1,000.

Local Bert Wilson, who owns a business two doors down from the cafe, said it was a dreadful blow to the town.

"When you get a dreadful situation like this - there was a lot of people who gathered on the street, but they were shunned back," he said.

The Queensland Ambulance Service treated 21 patients, 20 of whom were taken to hospital.

Eleven patients were driven to Atherton Hospital and three went to Innisfail Hospital, while the remaining six patients were airlifted to hospitals in Cairns and Townsville.