Approximately 35,000 people were evacuated from the towns of Superior and Louisville on Thursday. Estimates put it among the most destructive wildfires in Colorado history.

Authorities evacuated around 35,000 people from the towns of Superior and Louisville on Thursday as wildfires destroyed nearly 600 homes in Boulder County amid extremely high winds.

The Marshall fire had burned about 1,600 acres as of 5 p.m. after it sparked at around 11 a.m. at South Foothills Highway and Marshall Road, according to the Boulder Emergency Operations Center, which was activated to respond to the fire. 

The blaze destroyed at least 370 homes in the Sagamore neighborhood in Superior, 210 homes in Old Town Superior and several businesses, including the Element hotel and a Target store, officials said. 

As of 5 p.m., no deaths had been reported in connection with the fire; however, Boulder County Sheriff Joe Pelle said he "would not be surprised" if people were killed by the blaze. Officials said a police officer who responded to the fire was injured when his eye was hit by debris. 

"I've never seen anything like it, and we've had a lot of fires," Pelle said. "This is a horrific event." 

PHOTOS: Wildfires sweep through Boulder County, leave path of destruction

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Evacuation

A second, smaller fire, called the Middle Fork fire, had been burning near North Foothills Highway and Middle Fork Road since 10:30 a.m. It was not threatening any buildings, and officials had no estimate of how large that blaze was. 

If initial estimates were correct, the Marshall fire would be the most destructive wildfire in Colorado's history, behind the Black Forest fire, which destroyed 486 homes in 2013. The Cameron Peak fire — the largest wildfire in state history that burned over 208,000 acres — destroyed 224 homes.

The fire prompted Gov. Jared Polis to declare a state of emergency at 3:20 p.m. The declaration allows the state to access emergency funds and provide resources such as the Colorado National Guard, Colorado Division of Fire Prevention and Control and the State Emergency Operations Center.

"Gusts of 100, 110 mph can and have moved this fire down a football field in a matter of seconds," Polis said. "1,600 acres near a population center can be, and in this case is, absolutely devastating."

Polis said officials were unable to fly state helicopters and planes all day because of wind conditions.

The National Weather Service in Boulder said high winds were quickly spreading the flames, calling the conditions "life threatening" for people in Superior and Louisville. The area experienced gusts of up to 110 mph throughout the day, but winds were expected to calm down by Thursday evening. 

"The end won't come until the wind subsides," Pelle said. "This is not the kind of fire that you can fight head on." 

Authorities ordered mandatory evacuations for all of Superior, as well as for all of Louisville except for Old Town and north of South Boulder Road. Evacuations were also in place for Broomfield south of U.S. 36, west of Wadsworth Boulevard, west of Simms Street and south of Highway 128. In addition to official notices, anyone who can see the fire was asked to evacuate immediately. Evacuations were also ordered for the Meadow View community in Westminster Thursday night. 

Centura Health evacuated all patients from Avista Adventist Hospital in Louisville in the late afternoon. Patients were either discharged or transferred to Longmont United Hospital or St. Anthony North. Good Samaritan Medical Center in Lafayette evacuated 22 intensive care patients and six labor and delivery patients.

Pre-evacuation orders were in effect for the Via Varra and Skystone neighborhoods in Broomfield; west of Highway 287 between Arapahoe Road and Dillon Road in Lafayette; and the Meadow View community in Westminster.  Pre-evacuation orders formerly in place for the Arvada area were lifted as of 9:30 p.m. Thursday night. 

Authorities set up evacuation centers at the North Boulder Recreation Center at 3170 Broadway, the Longmont Senior Center at 910 Longs Peak Ave., the Lafayette YMCA at 2800 Dagny Way and the First Bank Center at 11450 Broomfield Lane. A large animal evacuation site was open at the Jefferson County Fairgrounds in Golden.

"If you’re in Boulder please stay home and off the roads if you can," the Boulder Police Department said in a statement. "We know the smoke is making it hard for drivers to see, clogging the roads, while first responders are handling multiple calls."

The Marshall and Middle Fork fires are believed to have been started by downed power lines, which were pushed over by extreme winds in the county, according to the Boulder County Sheriff’s Office. The investigation into the official cause of the fires is ongoing. 

Downed power lines sparked at least one other fire in Boulder County on Thursday morning in the 5000 block of North Broadway. That fire was quickly contained after spreading only 1 acre. 

All westbound lanes of U.S. 36 and northbound lanes of North Foothills Highway between Nebo Road and Ute Highway are closed due to the fire, deputies said.

U.S. Rep. Joe Neguse, a Democrat whose district includes Boulder and many of Denver's northwest suburbs, called the fires "unprecedented."

"Community members should follow guidance from the Boulder Office of Emergency Management and move to quickly evacuate as directed. Everyone in the area should practice the utmost caution," Neguse said in a statement. "Our office stands ready to assist families, local and state officials in any way that we can. I remain in close touch with Governor Polis and local and federal partners to ensure that every resource is made available to assist our communities in evacuation, fire management and recovery.”

U.S. Sen. Michael Bennet, a Colorado Democrat, echoed the sentiment.

"Coloradans, stay safe and follow evacuation orders. We stand ready to help with federal resources," Bennet said on Twitter.