A police officer and four firefighters were among those hospitalised after a truck carrying ammonium nitrate rolled over and exploded near Charleville in south-west Queensland.
A police spokesman said the blast was so powerful the truck "disintegrated", destroying two firefighting vehicles along with it and causing "catastrophic" damage to the Mitchell Highway.
The tanker, carrying more than 50 tonnes of the chemical, rolled on the highway about 30 kilometres south of Charleville just before 10:00pm (AEST) last night.
Firefighters were trying to extinguish the blaze when the truck exploded, injuring eight people, including four firefighters, a police officer, two bystanders and the truck driver.
Authorities said the two passers-by dragged the truck driver out of the vehicle.
The driver was airlifted to a Brisbane hospital in a serious condition.
The Queensland Fire and Rescue Service (QFRS) said two firefighters were still in Toowoomba Hospital and were considered "walking wounded".
The two other firefighters taken to Charleville Hospital had since been released.
The Mitchell Highway was closed in both directions and a two-kilometre exclusion zone remained in place around the scene.
Police were urging motorists to avoid the area until further notice.
Specialist officers were inspecting the crash site this morning.Truck 'disintegrated' in blast; firefighting trucks destroyed
The blast was so powerful, police officers had not yet been able to find any "specific" remnants of the truck, a spokesman said.
"When we were extricating in an emergency situation we could not locate any specific wreckage of the vehicle," Senior Sergeant Adrian Rieck said.
"This could be for a couple of reasons - one we were unable to conduct an appropriate assessment based on the amount of smoke and the ammonium nitrate and risk of further injury; we had to evacuate as soon as we could.
"The second issue for that is the fact that due to the type of explosion that the vehicle has disintegrated."
Senior Sergeant Rieck said he felt the explosion at his home in Charleville.
"The scene is likened to literally a bomb blast - it has caused catastrophic damage to the roadway and the highway," he said.
Senior Sergeant Rieck said officers were amazed no-one had been killed.
"We believe possible the location of the truck and where it's exploded and the construction of the roadway may have shielded them slightly from the majority of the blast, but there is a significant amount of debris that has been thrown a significant amount of distance from the initial explosive site," he said.
"It is certainly amazing that no-one was killed, but obviously a Godsend that that occurred."Earthquake coincided with explosion; both shook houses
Resident Jill Nelder said she thought she had felt the explosion from her house in Charleville.
"We were just sitting here talking and it was just like something sort of banged into the side of the house," she said.
"I just thought something had run into the side of my house - that's just what it felt like, it was a bang.
"We just got up to see what we could find and couldn't see anything.
"We walked round outside, but we couldn't find anything - gave us a hell of a fright."
However 20 minutes after the explosion, a magnitude 2 earthquake was recorded 55 kilometres south of Charleville.
Geoscience Australia seismologist Hugh Glanville said there was no link between the two incidents.
"We had reports of both the explosion and the earthquake because people get the house-shaking from both," he said.
"Often with a shockwave travelling through the air, you'll get your windows and doors rattling things like that.
"For a shockwave travelling through the ground, you'll get your floors, chairs and tables rattling.
"Also the time difference helps us to differentiate between the two [incidents].
"It's quite common for this area of Australia to get these occasional earthquakes of this size - it's quite a small one."