Thousands of people are being asked to evacuate immediately and hundreds of buildings have already been lost as winds fuel fast-spreading wildfires in Boulder County, Colorado.
Several small grass fires, sparked by downed power lines amid gusty winds in central Colorado, according to the Boulder County sheriff, have grown into raging blazes Thursday afternoon.
Of two wildfires burning, the most significant -- the Marshall Fire -- was first reported after 11 a.m. Thursday and has since "ballooned" to approximately 1,600 acres, Boulder County Sheriff Joe Pelle told reporters during a press briefing.
"We've been really concerned about the speed of the fire," Pelle said. "This was consuming football-field lengths of land in seconds."
Louisville, Colorado, with a population of about 20,000, is being asked to evacuate due to the Marshall Fire, according to the Boulder Office of Emergency Management. The entire city of Superior, Colorado, with a population of about 13,000 people, is also being asked to evacuate due to that fire.
Part of Westminster, Colorado, is also under a mandatory evacuation order, according to the city.
The National Weather Service of Denver/Boulder described the situation in Louisville as life-threatening in an alert on Twitter Thursday afternoon, while urging people to leave immediately.
Centura Health's Avista Adventist Hospital in Louisville started evacuating its patients, starting with its most critical, a Centura Health spokesperson told ABC News Thursday afternoon. Fifty-one patients were evacuated, with each being discharged or moved to another Centura Health facility. Several patients on ventilators were among those evacuated and moved to other hospitals, the spokesperson said.
"Avista Adventist Hospital has been a part of this community since 1895 and to see this level of devastation is heartbreaking for all of us," Isaac Sendros, chief executive officer for Avista Adventist Hospital. said in a statement. "Our hospital is in the center of a neighborhood that burned today. Despite what we saw outside our doors, our team was focused on quickly and safely evacuating our patients and staff."
Late Thursday night, The Broomfield Police Department announced the Broomfield Detention Center was evacuated. "All inmates have been evacuated & are safe," the department wrote on Twitter. "The inmates were moved to another facility. The Broomfield Detention Center is closed."
Hundreds of structures, including over 580 homes, are estimated to have been lost so far due to the fire, Pelle said.
Superior Mayor Clint Folsom told Denver ABC affiliate KMGH at least 200 structures, including residences, in the town have likely been lost.
"This is still a very active, fluid situation," he told the station.
The town evacuated quickly and Folsom said he was not aware of any injuries or deaths.
Six patients were taken to UCHealth Broomfield, which serves the Boulder area, due to injuries from the fires, a hospital spokesperson confirmed to ABC News.
One officer had a minor injury to his eye due to windblown debris, according to Pelle, who said he was not aware of any other injures or fatalities at this time.
"However, I'd like to emphasize that due to the magnitude of this fire, the intensity of this fire and its presence in such a heavily populated area, we would not be surprised if there are injuries or fatalities," he said.
Both fires were likely caused by downed power lines, Pelle said.
"We had deputies in the area who confirmed there were downed power lines. So we believe that's what caused the fire," he said, adding that authorities will likely determine the exact cause in the next couple days.
Colorado fire officials told ABC News that the high winds are making it difficult to get aerial resources into the area to fight the fires.
Wind gusts topping 100 mph were reported in northern Jefferson County earlier Thursday, while parts of Boulder County saw gusts over 80 mph. The city of Boulder also reported wind gusts over 70 mph Thursday afternoon.
The Boulder area is currently suffering from extreme drought, according to the National Oceanic and Atmospheric Administration and the Department of Agriculture.
Colorado Gov. Jared Polis has declared a state of emergency due to the fires in Boulder County, his office said.
"Prayers for thousands of families evacuating from the fires in Superior and Boulder County," Polis tweeted. "Fast winds are spreading flames quickly and all aircraft are grounded."
ABC News' Jeff Cook, Dan Manzo, Jenna Harrison and Dan Peck contributed to this report.