Bigger and more "explosive" wildfires are raging across the U.S. West, with the area burned in Colorado already four times the size of last year's total, as rising temperatures, drought and a buildup of forest fuels supercharge blazes.

So far this year 3.3 million acres have burned in U.S. forests, just below the figure for this time in 2017. Last year was the second worst year on record with 10 million acres blackened, according to the National Interagency Fire Center (NIFC).

Around 2,600 homes have been destroyed nationally by fires year to date, according to Forest Service data. Ten U.S. wildland firefighters have been killed up to this week, compared with 14 killed in all of 2017, according to the National Wildfire Coordinating Group. It was not immediately possible to verify how many civilians have died this year.