Firefighters across Colorado battled intense heat and dangerous conditions on Thursday in a battle to gain control of several blazes that forced hundreds of evacuations, destroying several homes and causing at least one death.

Four major wildfires started burning between Monday and Wednesday and have raged across thousands of acres of dry land, fueled by intense heat and strong wind gusts. The fires were sparked along the foothills of the Front Range, a part of the Rocky Mountains that runs from central Colorado into Wyoming, passing near several major cities including Denver.

Together, the Alexander Mountain Fire, Stone Canyon Fire, Quarry Fire and Lake Shore Fire have burned over 9,000 acres, and vary widely in size, with the Alexander Mountain Fire and Stone Canyon Fire claiming the vast majority of territory. However, the Quarry Fire and Stone Canyon Fire are burning closer to Denver and the town of Lyons, north of Boulder.

On Thursday, thousands were under evacuation orders as several wildfires remained near 0% contained. The Denver area was covered in a thick layer of smoke, and temperatures are expected to reach a sweltering 98 degrees Fahrenheit on Thursday, according to the National Weather Service.

“Everybody should be worried right now, there’s a huge fire and it’s difficult to fight," said Jefferson County Public Affairs Director Mark Techmeyer at a press conference Thursday morning.

The Colorado Department of Public Health and Environment urged residents in the Front Range corridor to limit their driving, saying exhaust from non-electric cars will negatively affect air quality, which could reach "unhealthy" levels from "ozone and fine particulate matter concentrations."

In California, the Park Fire continued spreading in the northern part of the state and was 18% contained as of Thursday, according to Cal Fire.

Firefighters battle tough terrain

Officials in Jefferson Country, Colorado, which includes parts of Denver, said Thursday that firefighters are working desperately to control the flames, but that steep terrain is making their jobs harder. Techmeyer said in all his years responding to wildfires in Colorado, the massive Quarry Fire is "one of the tougher ones" because of steep gulches that force firefighters to make grueling climbs.

“This fire is not going to be won in the air. Because of the terrain, this will be won on the ground," Techmeyer said.

Firefighters managed to prevent the fire from growing Wednesday night, Techmeyer said, and no structures were lost.

Five fighters were injured Wednesday, Techmeyer said, four from heat exhaustion and one who suffered a seizure.

Fire-battling resources are thin in and around Denver, officials said Thursday, because everyone is already deployed against the flames. Techmeyer likened the conflict to a tough football game, in which a coach can't rely on a deep bench of backup players.

“Somebody goes down, it’s difficult," he told reporters Thursday.

Fire could worsen if it jumps major road

In Jefferson County, emergency responders said their top goal is preventing the Quarry Fire from jumping across Deer Creek Canyon Road, which runs southwest to northeast through parks, ranches and scenic areas west of Denver.

Techmeyer said Thursday morning firefighters are working intensely to prevent the fire from spreading north across the road.

“This fire cannot jump over to the north side," Techmeyer said. "We’ll have a whole other situation on our hands if that happens."

Park Fire rages in California

On Thursday, more than 6,000 firefighters and 40 helicopters were deployed against the Park Fire, which continued to burn over 390,000 acres.

California also received resources from Utah and Texas to help battle the flames, according to Cal Fire, as dangerous fire weather conditions rapidly escalate in mountain canyons just east of Chico, California.

Cal Fire said Thursday a devastating combination of heat, low humidity and dry winds could make the fire worse in coming days.

"Today will mark the first of several days where fire weather will become increasingly critical," Cal Fire said.

On Thursday, temperatures are expected to reach the 90s and low 100s, according to Cal Fire, and humidity will drop to under 20%.