For two days straight, with barely time for sleep, Ron Earls and his team of firefighters battled a monster blaze this week that spread out of control in a small California town.

"We were out here for almost 50 hours," Earls told AFP, standing amid still-smoldering ruins of homes consumed by the flames in Middletown, in Lake County.

"The adrenaline kicks in and you are not that tired," added Earls, soot streaking his face and coating his flame-resistant yellow jumpsuit.

A member of his crew hefted a large axe as they doused hot spots and hacked away charred beams at risk of falling.

The so-called Valley Fire, one of the worst wildfires in California history, destroyed more than 500 homes and displaced thousands after it erupted on Saturday, stunning even seasoned firefighters as it spread at lightning speed, whipped by high winds.

Similar wildfires have waged a relentless campaign in the drought-stricken western United States this year, mobilizing some 30,000 firefighters, National Guard units and rescuers from across the country.

Beyond the millions of acres consumed by the flames that have killed three residents in California, firefighters in the region have paid a steep price with several killed in the line of duty.

- Relentless infernos -

The grueling battle with the wildfires have also left firefighters physically weary, emotionally drained, and hoping for an early start to a soggy rainy season.

"We have had multiple major fires this year with very few breaks in between," CalFire incident commander Barry Biermann told AFP.

"Our firefighters are getting tired. Fatigue is always a factor."

Before getting the call for help in battling the Valley Fire, Earls spent 41 days fighting a different wildfire. That blaze was in steep canyons that had filled with smoke, making breathing difficult.

"We had three days off and we were already itching to get back out there," Earls, who is based near Los Angeles, said with a nod to other members of his team.

"People really do love this job."

Teams typically work 21-day stints, on fire lines for 24 hours straight followed by a day off. Fires can be in regions so remote that firefighters grab what sleep they can at base camps instead of trying to make it to the comfort of a hotel bed.

"Working in these environments and moving from fire to fire is exhausting," CalFire battalion chief Mike Smith told AFP.

- Always on guard -

Four firefighters from a helicopter crew were hospitalized this week after the flames turned on them.

"You always try to keep a heads-up. You keep a lookout," Earls said.

"Unfortunately, things happen and people are caught off guard."

While firefighters can't train for sleep deprivation, they train to handle punishing heat and the rigors of days spent on scorching, smoky, rugged terrain.

"We train like the army," Fernando Herrera of CalFire told AFP.

Firefighters also face the emotional stress of knowing their own families must fend for themselves, and of comforting people who have lost their pets, or livestock.

At least eight firefighters have lost their own homes to the flames.

"I don't think that it will hit some of these individuals until this is over and they sit down and think about what they just went through," Biermann said.

CalFire battalion chief Paul Duncan was at a fire in the town of Cobb about 20 miles (32 kilometers) from his home when his own house burned to the ground.

"I would have gone to Cobb even if I'd known the outcome at my own home," Duncan said.

"Of course, I would have loaded up my truck with more things and gotten my family out of there sooner."

Firefighters are hoping cooler temperatures and rain expected on Wednesday will deliver a knock-out blow to the Valley Fire before the weather shifts back to hot, dry and windy conditions during the weekend.

"We are not out of the woods yet," chief Smith said.

"We are still in a very dangerous situation."