A fast-moving wildfire near Fort Collins in the US state of Colorado has scorched nearly 37,000 acres (14,973 hectares) of land, officials say.
The fire has not been contained and sheriff's officials described conditions as "concerning".
Hundreds of residents have been evacuated and 18 structures have been burned or damaged in the blaze.
Meanwhile, a wildfire in New Mexico has covered 25,600 acres and damaged or destroyed up to 35 structures.
In Colorado, more than 400 firefighters are on the scene, Nick Christensen, executive officer of the Larimer County Sheriff's Office, told reporters.
Five heavy air tankers, helicopters and military aircraft are now combating the fire, he added.
The fire is moving rapidly at a pace of 1mph (1.6km/h) and homes have been damaged in the neighbourhoods of Rist Canyon, Stove Prairie, Paradise Park, Poudre Canyon and Poudre Park, he added.
One person has been reported missing and is still unaccounted for, Mr Christensen said, adding that authorities were investigating the person's whereabouts.
The wildfires have generated dense smoke, which has spread as far as Nebraska, Texas and western Kansas, the Associated Press reported.
Officials in New Mexico also confirmed that hundreds of residents had been evacuated from the town of Ruidoso and have said the nearby town of Capitan could also face evacuation.
New Mexico Governor Susana Martinez deployed 100 National Guard troops on both Saturday and Sunday to help with the evacuation effort.
-BBC
