The crash caused a gas bottle to explode which set fire to the Serves You Right Cafe in Ravenshoe, south of Cairns, in Queensland state.
Three people are in critical condition and have been airlifted to hospital. The driver is among the injured.
It is not known what caused the vehicle to veer off the road.
Patients were being treated for a "varying degree of burns" said Queensland Ambulance Service Assistant Commissioner Rod Sheather. The fire took an hour to bring under control, he said.
Kate Lewis, who works at a supermarket across from the cafe, described the scene as horrific.
"We just heard a massive sonic boom and went running out and saw the cafe on fire and lots of burned people," she told the Australian Broadcasting Corporation.
Ravenshoe, a farming town, has a population of about 1,000 people.
Nineteen people have been injured when a pickup truck crashed into a cafe in northern Australia, causing a fire that engulfed the building, police said.