Bushfires that have closed major highways on the Nullarbor could end up costing the economy millions of dollars and cause widespread food shortages, with the situation set to get worse before it gets better.

Key points: A catastrophic fire danger rating has been in place with very hot, dry and windy conditions

A catastrophic fire danger rating has been in place with very hot, dry and windy conditions The only sealed road between WA and SA is likely to remain closed for another five days

The only sealed road between WA and SA is likely to remain closed for another five days Authorities are turning back west-bound traffic with supply issues to roadhouses becoming dire

About 140 firefighters are battling eight fire fronts that have cut off the small WA town of Norseman, about 700 kilometres south-east of Perth, for extended periods since the first blaze began on December 16.

The situation escalated recently when authorities advised the Eyre Highway — the only sealed road linking Western Australia and South Australia — would be closed for at least the next five days.

A fire emergency, which has since been downgraded, was also declared for the Balladonia Roadhouse, which is located 220 kilometres east of Norseman and 155 kilometres to the west of the Caiguna Roadhouse, where about 250 truck drivers and holidaymakers have become stranded.

Authorities are turning back west-bound motorists at Eucla, 12 kilometres west of the South Australian border, because the supply situation at roadhouses along the 1,660-kilometre-long Eyre Highway has become dire.

Fire authorities provide an update to people stranded at Caiguna Roadhouse. ( Supplied: Denise Leppard/West Aussie Nomads )

Department of Fire and Emergency Services incident controller Peter Sutton said the catastrophic fire conditions in the region were not helping, with the mercury hitting 47 degrees Celsius in Caiguna yesterday.

"We are seeing new fires each day and are expecting a lightning belt to come through here soon with dry lightning and we expect that will start additional fires," Mr Sutton said.

"We've got 140 firefighters on the ground, 20 machines are working, and those machinery operators, I've just got to commend them and also the firefighters who are working in very, very trying conditions.

"We had eight aircraft within the fire zone, which include four waterbombers and they are doing an amazing job for us."

Food, medicine shortages tipped in Perth

Emergency supplies, including medicine, are being brought in to Norseman and Caiguna.

The peak body for road transport companies in WA warned the bushfires would start to have an impact on food prices and possibly medicines in Perth.

Loading

"Things that we are bringing across from the east … things like cherries, stone fruit, watermelon, pumpkin, they'll run into short supply," Western Roads Federation CEO Cam Dumesny said.

"Even some of your temperature-controlled medicines. We'll start having shortages of those or certainly interruptions to those into WA.

"On the other side of the coin, our seafood, avocado and lettuce producers are having problems because we can't get their produce to market on the east coast."

Mr Dumesny said the cost to businesses and the wider economy will be enormous, saying one of the bigger transport companies had about 50 trucks on the road when the fires started last month.

"They're holding a lot of their road trains back in anticipation of the roads being reopened, but it does leave some of our drivers stuck out there without too many alternatives," he said.

"It's a major problem."

Both Woolworths and Coles have warned shoppers to expect food shortages.

Signs were put up at Woolworths in Palmyra warning customers of the situation. ( Supplied )

"Due to the closure of the Eyre Highway and the Coolgardie-Esperance Highway, our WA customers may see shortages of a range of fruit and vegetables over the coming days," a Woolworths said in a statement.

Coles said a number of trucks carrying fresh produce to its Perth distribution centre had been delayed by the road closures.

"We are rerouting deliveries and using rail where possible, however availability of some fresh fruit and vegetable lines may be impacted in coming days," the company said.

The supermarkets apologised to customers for the inconvenience and said they were "working hard" to re-stock shelves as soon as possible.

Truck drivers in for long haul

The ABC spoke with truck driver Tim Buckland in Coolgardie, where he has been stuck on the side of the highway for the past four days.

Truck driver Tim Buckland has been stuck in Coolgardie for the past three days. ( ABC Goldfields: Jarrod Lucas )

Coolgardie is nearly 200km from the fire front at Norseman, but it is where the road blocks begin.

Loading

Mr Buckland dropped off a load of bananas in Perth and was heading home to Tully in northern Queensland.

"We knew about the road closures when I left Perth, but we didn't imagine there would be this much of a delay," he said.

"We just came out in the hope it would be open when we got here.

"I'd rather be stuck here than stuck in the middle of a bushfire."

Mr Buckland praised the hospitality of locals in Coolgardie who he said had welcomed the fleet of truck drivers with open arms.

He described the Nullarbor road closures as unprecedented, and said he was happy to wait to avoid a repeat of the Boorabbin bushfire disaster on New Year's Eve 2007, when three truck drivers died after driving into a firestorm along the Great Eastern Highway.

"I've been doing this for 10 years and I've never had anything like this," he said.

"I've been held up with floods in NSW before, but nothing for this amount of time.

"There's nothing we can do about it, so we've just got to wait until it's safe to continue on and let the firies get on with their job.

"I'm quite happy to stay here until I'm told it's safe."

Loading

Loading

Perth truck driver Chris Fullgrabe is heading to Melbourne and said he always carried enough food and water to sustain himself in the case of a remote breakdown.

He had been parked in Coolgardie for 36 hours when he spoke to the ABC, and said he had also been stranded for three days at Balladonia before Christmas.

"If my boss wants me to wait here three days, I'll wait three days," he said.

"It is frustrating, but the service stations here do a great job, there are showers for truck drivers and people travelling in caravans, so you've just got to have a bit of patience.

"A few [trucks] have gone back [to Perth], but there's still a few waiting around, but at the end of the day it's up to your bosses as to whether you stick it out."

Roadhouses running on empty

Perth man Jason Leppard was on the last leg of a three-year caravan trip with his wife, daughter, and dog when they became stuck at Caiguna Roadhouse.

A lighter moment at Caiguna where about 250 people have been stranded during the bushfire crisis. ( Supplied: Denise Leppard/West Aussie Nomads )

He said the crowd had thinned since authorities told people about the extended road closures.

Loading

"We were travelling from Ceduna, heading west back home and we've been holed up here for three days," he said.

"We have a pup on board as well so that's another mouth to feed.

"We had a meeting and it was suggested if it was non-essential to head west, turn around and go back east, which did clear out some of the people."

Caiguna Roadhouse has had emergency supplies flown in after running out of toilet paper on Wednesday.

"There's quite a restriction on the water supply from the roadhouse," he said.

"Bottles are on sale but they're quite expensive at $6 a pop for a litre and a half.

"Tap water, which is drinkable, just trickles out.

"The basics we need are toilet paper and soap otherwise you've got another health issue that's going to pop up and cause all sorts of problems."