(Reuters) – A wildfire raging largely unchecked on Wednesday in southwest Colorado forced hundreds of residents to prepare to evacuate and could spread to other states, officials warned.

Emergency crews said they had only managed to contain 10 percent of the fire near the towns of Durango and Hermosa, where the forecast was for another dry, hot day, with wind gusts likely to spread the fire.

The fire grew about 1,000 acres from Tuesday to Wednesday, to cover 4,015 acres (1,625 hectares). It is expanding to the north, the west and the south but has not crossed U.S. Highway 550, which has helped firefighters protect 825 houses east of the highway, said Megan Graham, spokeswoman for La Plata County.

Residents of those 825 houses were ordered to evacuate several days ago, after the fire started on Friday.

La Plata County has issued pre-evacuation notices for about another 1,250 residences, Graham said.

Vehicles are being allowed to travel through the area on Highway 550 in single-file convoys protected and escorted by law enforcement officers, Graham said.

“Please do not stop to take photos and observe the fire! Stay with the convoy!” a Twitter message posted on Wednesday by La Plata County warned.

FOUR CORNERS REGION

The 416 Fire – named, local media said, after its official incident number – burned over steep terrain sending smoke billowing into the sky.

Investigators have yet to determine the cause of the blaze, said Cam Hooley, spokeswoman for the San Juan National Forest.

The Durango Herald reported that a retired volunteer firefighter noticed the fire last Friday morning.

The National Weather Service has placed large sections of the Four Corners region of Colorado, New Mexico, Arizona and Utah under an elevated fire risk.

In New Mexico, the Ute Park wildfire was 30 percent contained by Wednesday morning, having burned 36,800 acres (14,892 hectares) of drought-parched grassland and timber since last Thursday. The 1,110 residents of Cimarron, New Mexico, were on Monday allowed back into their homes after showers on Sunday helped quell part of that blaze.

No injuries or major damage to structures have been reported from either fire.

(Reporting by Bernie Woodall in Fort Lauderdale, Florida, Jon Herskovitz in Austin, Texas and Brendan O’Brien in Milwaukee; Editing by Bill Tarrant and Lisa Shumaker)