Investigators have been granted access to the site of a catastrophic truck crash and explosion that injured eight people south of Charleville in south-west Queensland.

The truck driver, two fire officers, and two passers-by remain in hospital with serious injuries, while three other rescue workers were recovering at their homes in Charleville.

Emergency crews have described the scene as "war zone", with the explosion leaving a five-metre-wide crater in the landscape.

A two-kilometre exclusion zone was declared after the truck, carting more than 50 tonnes of ammonium nitrate, crashed and rolled about 10:00pm (AEST) on Friday.

Police said the blast was so powerful it "disintegrated" the truck, destroyed firefighting vehicles and two bridges, and blew a hole in the Mitchell Highway.

Authorities said it was a miracle no-one lost their life.

The site of the explosion was deemed too unsafe for authorities to enter on Sunday, but police and forensic experts have now been granted access.

Fire Inspector Warren Buckley said investigators would be looking at the incident for some time.

"You have a look at the road behind you and there is no road behind you - it's going to take weeks, if not months, to clean up," he said.

"This is a first in 26 years of firefighting - it's not often we come across these major events and our crews are extremely lucky."

Assistant Fire Commissioner Tom Dawson praised the actions of the officers.

"Without doubt, the courage shown by the crews and to experience this experience and survive it - I've got the greatest admiration for those on scene," he said.

Three remain in hospital

The 33-year-old truck driver was in an induced coma at the Royal Brisbane Hospital, with his pregnant wife by his side.

Two firefighters remain in the Toowoomba hospital with internal bruising and serious damage to their ear drums and were in a stable condition.

Highway construction work may have shielded emergency workers from the full force of the blast. ( Supplied: Queensland Police Service )

Rescue crews were trying to extract the driver from the truck when they found out there was ammonium nitrate inside.

They were making a mad dash from the truck when it exploded.

Inspectors said it was the slight rise of 1.5 metres from where the truck rolled under the bridge to where they were standing that ultimately save their lives.

It was the second accident in Queensland involving transportation of the hazardous chemical. The last was in Taroom in 1972.

The owner of the truck, Kalari, said it was deeply saddened that people were injured in the explosion and that their welfare was the company's priority.

In a statement, Kalari said it had stopped the service route pending more information about the incident.

Authorities preparing 100-kilometre detour

Queensland Transport Minister Scott Emerson said officers from his department were investigating the accident and the road would be closed for some time.

The Department of Main Roads was preparing a 100-kilometre detour to Cunnamulla for traffic in the area, along the Charleville-Bollon Road.

"There are rules in place both in terms of signage and particular routes that they are allowed to carry dangerous goods and obviously we'll be talking to police about whether anything was done wrong," Mr Emerson said.

"The road will remain closed indefinitely until the area is deemed safe.

"The Department of Main Roads is still working on an interim detour."