Denver, Dec 31 (IANS): The Marshall wildfire in Boulder County, Colorado, dubbed as the most devastating in the US state's history, torched some 600 structures just after five hours it erupted, according to the National Weather Service (NWS).

Wind blasts of 110 miles per hour took down power lines and ignited parched field grass below on Thursday, Xinhua news agency quoted the NWS as saying.

As winds continued throughout the day, the blaze swept unchecked through affluent subdivisions in the Louisville area before heading south to nearby Superior, according to fire officials, who admitted the speed had caught them unprepared.

Colorado Governor Jared Polis has declared a state of emergency as thousands of local residents were ordered to evacuate.

"Tens of thousands of people in the area have been evacuated and hundreds of structures, both homes and businesses, were lost," Boulder County Sheriff Joe Pelle told a press conference, adding the blaze has consumed 1,600 acres.

No casualties had been reported as of 6 p.m., but Pelle warned that with a fire of this magnitude and speed, he would not be surprised if injuries or fatalities were later discovered.

Fire crews from metro Denver and Boulder have been called into the Boulder County area to assist.

US media estimated that homes in the Louisville area averaged $862,000, while the median Superior home cost is $775,000.

The Federal Emergency Management Agency said it has authorized the use of federal funds to help with firefighting costs, according to NBC News.