At least 19,000 people were under mandatory evacuations Saturday as a fast-moving wildfire burned in the Boulder, Colorado, area, authorities said.
No injuries were reported and it wasn't immediately clear if any structures were threatened, but the blaze near the National Center for Atmospheric Research's Mesa Laboratory & Visitor Center had doubled in size in a few hours Saturday afternoon.
The Boulder Office of Emergency Management tweeted that those ordered to leave included people connected to about 8,000 homes near the blaze. Large animals were being accepted at Boulder County Fairgrounds, authorities said.
Boulder Fire Rescue spokeswoman Marya Washburn said the day's warm weather and strong winds were giving way to more favorable conditions on the front lines.
"The wind is now dying down, and we’re expecting the weather to work more in our favor," she said Saturday evening.
On Sunday, the fire was at an estimated 200 acres with about 21 percent contained, according to Mike Smith, incident commander with Boulder County. Authorities had no reports of injuries or missing people by Sunday morning.
Firefighters were aided by low wind speeds that allowed for air support and relatively humid weather overnight, Smith said.
"We will continue to reinforce the line to make sure that the fire doesn't move towards the city or down towards Eldorado Canyon," Smith said. "We're gonna continue to try and corral this fire up into the rocks into the snow, which is really one of our big holding features right now and one of the reasons that we're having really, again, good success."
Authorities investigating the blaze's origins said it began south of the Mesa Laboratory, where there's a watershed, canyon and trails that cross from east to west, toward the Rocky Mountains.
"The fire started this afternoon down in the Bear Creek drainage," Brian Oliver, chief of the Boulder Fire Rescue Wildland Division, said at an evening press conference.
Emergency management officials said Boulder County Sheriff's Office investigators were looking for potential witnesses who may have been on or near the trails south of the Mesa Laboratory around 2 p.m.
Evacuations for the area were still in place on Sunday, Washburn said. Some areas were out of the evacuation zone but routes to get there were still considered unsafe. Firefighters were working on clearing those routes Sunday, Washburn said.
Air tankers were seen on video from NBC affiliate KUSA of Denver dropping retardant on the blaze.
Washburn said protecting homes and buildings was the top priority for now. "We’re doing everything we can to keep structures safe," she said.
Boulder police said earlier that people who signed up for cellphone emergency alerts and who were within a quarter mile of the Mesa Laboratory received wireless alerts ordering them to leave the area as the wildfire started moving rapidly.
Saturday's blaze is not far from the area burned by the most destructive wildfire in state history, the Marshall Fire, which started Dec. 30 and burned into 2022.
It consumed nearly 10 square miles, destroyed 991 homes and damaged 127 other structures. The cause remains undetermined, although a Boulder Open Space and Mountain Parks ranger wrote a report that includes the possibility it had two ignition points.