JEFFERSON COUNTY —A small blaze erupted in the foothills west of Denver on Monday, prompting the evacuation of thousands of people and threatening at least 100 homes, fire officials said.

By 8 p.m., the Bluebell fire had grown to between 25-35 acres. It was burning on private property about a mile from the Arapahoe National Forest. Many evacuees were allowed to go home Monday evening, but people living past Hemlock Lane off of Brook Forest Drive were to remain evacuated overnight. Residents in 143 homes were still evacuated.

Officials did not yet have containment, but the fire “is currently laying down,” according to the Jefferson County Sheriff’s Office.

A helicopter dropped water on the fire near Evergreen, a single-engine air tanker dumped fire retardant and six local fire protection crews worked the blaze on the ground.

The fire was reported about 2 p.m. Monday at 33528 Bluebell Circle, said Mark Techmeyer, a Jefferson County Sheriff’s Office spokesman said.

About 100 homes were threatened, but no structures were damaged. The cause of the blaze was not known.

“It’s not a monster yet, and maybe it won’t be,” Jacki Kelley, spokeswoman for the Jefferson County Sheriff’s Department, said earlier in the day. “People are on the ground and firefighters are working to help stop this.”

She added, “We had a hot, dry, windy day on the mountain, and we have a fire in a wooded area that’s well-fueled.”

Evacuations were ordered for a 4-mile radius around the fire, Techmeyer said. The evacuation areas included: U.S. 285 on the south; Buffalo Park Road on the north; County Road 73 on the east; and the Jefferson County line on the west. Areas being evacuated include homes along Brook Forest Drive.

An unknown number of homes were also evacuated in adjacent Clear Creek County.

Some 9,900 emergency calls were made using Jefferson County’s “CodeRED” notification system. The sheriff’s office tweeted “Leave NOW!”

More than 150 people gathered at an evacuation center at Conifer High School, where they anxiously awaited more information. Families huddled next to parked cars, trucks and trailers while they called friends and loved ones.

Eric Westerhausen and his family have been evacuated to the parking lot before. Westerhausen was in Denver when he received an emergency notification telling him and his family to leave their home — which is located south of the blaze — immediately.

“We’ve been told to leave before, so this time we just got out. Period,” Westerhausen said. “After the way everything happened last year, we weren’t waiting for anything.”

Taylor Jones and her boyfriend, Mike Fisher, closed on their house in Evergreen three weeks ago and were working from home Monday when they were evacuated. Their home is on Brook Forest Drive.

They’d been planning to do fire mitigation and remove firewood and carpet from the side of their home, but they hadn’t gotten around to it yet. On Sunday night, they sat down to create a fire plan.

When they got the evacuation call Monday, they had only enough time to grab their two dogs, seven chickens and two parakeets.

“I was crying and I was panicked because this was our worst fear,” Jones said.

In March 2012, residents were also evacuated to the high school when the Lower North Fork Fire broke out.

Traffic was stop-and-go on Colorado 73 as evacuees streamed out of the area, many carrying crates of dogs, cats, goats and rabbits. Smoke hung over the region.

The Red Cross sent a Mass Care Team to Conifer High School around 6 p.m., according to the organization’s local spokesman Bill Fortune.

The team will help provide refreshments initially, and are prepared to turn the evacuation center into a shelter and provide cots, blankets and other necessities if needed.

“We’re monitoring the situation and taking requests as they come,” Fortune said.

Large animals are to be evacuated to the Jefferson County Fairgrounds, 15200 W. 6th Ave. Service Road in Golden.

John Orlando, who lives a quarter-mile from the fire, had to evacuate seven horses, two cats and two dogs.

“There was enough fire to scare the hell out of you,” Orlando said. He described the fire as “more frantic” compared to last year’s fire near Evergreen.

Smaller animals were evacuated to The Foothills Animal Shelter, 580 McIntyre St., in Golden.

“We are preparing to bring animals in,” said Heather Cameron, the shelter’s leader.

Evergreen, Elk Creek, Lower North Fork and Inter-Canyon fire departments are fighting the fire, which was burning north of the Brook Forest area and west of Evergreen Heights and Estates.

The 25-30 mph gusts blowing from the southwest were not a large factor in the fire, according to The National Weather Service.

“We shouldn’t worry too much about strong winds, at least tonight,” said Dan Leszcynski, a meteorologist with the service. “It’s not really real dry, which is a good thing.”

Moisture is expected Tuesday evening, he said.

Adrian D. Garcia: 303-954-1729, agarcia@denverpost.com, twitter/ adriandgarcia

Staff writer Kieran Nicholson contributed to this report.