UPDATE: Crews have made some progress against a small wildfire just west of downtown Boulder, Colorado.
The blaze has burned just over 60 acres, and it was 20 percent contained Sunday afternoon. Officials have made more than 1,000 calls to residents to evacuate and thousands more to others to be prepared to leave if conditions worsen.
Officials with the Boulder Office of Emergency Management say fire crews are feeling good about the progress but are still concerned about stronger winds forecast later in the day.
The National Weather Service has issued a warning predicting warm, dry weather and winds gusting up to 40 mph into this evening.
Boulder County officials say the fire is being fought predominantly from the air.
There are no reports of damage to homes.
UPDATE: Authorities have made more than 1,000 calls to residents in and around Boulder, Colorado, ordering them to leave their homes as a wildfire burns in the mountains just west of the university town.
Gabi Boerkircher with the Boulder Office of Emergency Management says an additional 2,200 reverse 911 calls early Sunday warned others to get ready to leave if conditions get worse.
It wasn't clear exactly how many houses or residents were evacuated because the calls could have gone to multiple people living in the same home and likely didn't include children.
The fire reported around 1:40 a.m. Sunday had burned 30 to 50 acres just a couple of miles from downtown Boulder. Several aircraft are making drops to battle the flames.
Emergency officials don't know how the fire started.
BOULDER, Colo. (AP) - Authorities say a small wildfire burning in the mountains just outside the Colorado city of Boulder has forced people from their homes and is filling the sky with smoke.
Wind is pushing the flames early Sunday just a couple of miles from the downtown area. The fire was only 30 to 50 acres.
Shannon Cordingly of the Boulder Office of Emergency Management says it's unclear how many homes have been evacuated just west of the university town and how the flames ignited.
The agency says there are no reports of injuries or buildings destroyed. Cordingly says if the fire keeps spreading, more evacuations are possible.
Resident Seth Frankel, who's packed after being warned he may need to evacuate, says dead trees "are exploding into a black plume that goes into the air."