The site of an ammonia truck explosion near Charleville in Queensland's south-west is still too unsafe for authorities to enter, Queensland Fire and Rescue Service (QFRS) says.

A two-kilometre exclusion zone remains in place at the scene of the blast, which occurred after a truck carting more than 50 tonnes of ammonium nitrate crashed and rolled about 10:00pm (AEST) on Friday.

Eight men, including a police officer and four firefighters, were injured in the blast, which police said was so powerful it "disintegrated" the truck, destroyed two firefighting vehicles and two bridges, and blew a hole in the Mitchell Highway.

Two motorists who stopped to help were also injured and the truck driver remains in a critical condition with serious burns and head injuries in the Royal Brisbane Hospital.

Two rescue workers remain in the Toowoomba hospital with serious internal bruising and damage to their ear drums.

Shockwaves from the blast were felt by residents in nearby towns, and the local fire chief described the fact no-one died as "a miracle".

Tom Dawson, the Assistant Fire Commissioner for the south-west region, said a team of experts gathered in Charleville this morning to determine the best way to stabilise the blast area.

"We still actually believe we've got a little pocket of ammonium nitrate burning, so that in itself, with the fumes that'll come from that burning process, still indicates we've got an unstable situation," he said.

"It's going to be a very scientific call to say it is now stable, then we'll go about it very guardedly to go closer to determine the degree of safety.

"We now believe a lot of the product is actually buried under earth."

Assistant Fire Commissioner Dawson said the devastation from the explosion was immense.

"We're talking up to two to three kilometres of damage to foliage, structures, the rail bridge, the bridge itself," he said.

Police said motorists should avoid the area while specialist officers examine the scene.

A 600-kilometre detour is in place.

Workplace Health and Safety officers would conduct their own investigation into the explosion.

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.

600km detour in place; damage to affect transport industry

The Queensland Trucking Association (QTA) said the road damage would cause big problems for the national transport and heavy vehicle industry.

QTA spokesman Peter Garske said the Mitchell Highway connected several states.

"My understanding is they expect to have up - in a fairly short space of time - a side track, but that will only be suitable to motor vehicles; it will not be suitable to heavy vehicles," he said.

"It could be quite some days before a route in and around the Mitchell highway for heavy vehicles [is available].

One of the fire trucks damaged in the explosion near Charleville. ( QFRS )

"It will conceivably be weeks or months before the infrastructure is properly restored to its original condition."

Mr Garske said the accident was a warning to companies hauling dangerous goods.

He said the extent of the damage would resonate in the industry.

"It is a wake-up call to everybody in the industry - whether it is a heavy vehicle owner or whether it is a heavy vehicle driver or indeed the customers, the owners of the freight, the consignors the consignees - we all have a responsibility in the safe movement of heavy vehicles in Australia and the safe carriage of the freight," he said.

Mr Garske said he had never seen an accident like it in Australia.

"I have been involved in this industry for 20 years now and to my knowledge an incident of this type and this size has not occurred anywhere in this state and to the best of my knowledge Australia in that 20 years," he said.

No concerns over road transport of chemicals: fire chief

Firefighters said the damage and destruction caused by the truck explosion was rare.

Assistant Fire Commissioner Dawson said trucks hauled dangerous chemicals and fuels on Australian roads every day and it was not a problem unless they crashed.

"This product - and trucks like this very same truck - travel these roads every day," he said.

"Every day they're out there and they don't go bang.

"Something's happened to bring this truck in a situation, which has possibly mixed the product on the back of the truck - maybe with the diesel fuel, the impact of the initial [crash] when it goes off the road - so those circumstances have had more of a connection to the end result.

"You'd be surprised - there's a lot of these trucks - they do it very safely and very effectively.

"It's when they leave the road there is a problem."

Fears region has lost tourism and trade

Murweh Shire Council Mayor Dennis Cook said damage to the Mitchell Highway would affect tourism and trade in the region.

He said the Department of Main Roads needed to act quickly.

"We have lost our tourist trade as well, because the main road is gone," he said.

"We need to do a bypass of some description before we even put the bridge back together because it will take a while.

"We need someone to find some emergency money to get moving on this because this is what we need. It is our main thoroughfare through the west."

Queensland Transport Minister Scott Emerson said his department was working as fast as possible to open an alternative four-wheel-drive track around the explosion site.

"We will assess the situation is," he said.

"I think there will also be some sort of insurance pay-outs as well as part of this process - that's the advice I've received.

"Until we can get into the site and assess what the damage is, it very difficult to say what the job will require."