A fast-moving brush fire in a suburban community north of Los Angeles destroyed one home on Monday and threatened thousands more, though officials said calmer winds had slowed fire activity by nighttime.

The blaze in Simi Valley, Calif., about 40 miles northwest of downtown Los Angeles, began just before 11 a.m. on Monday and grew to 1,364 acres by the evening, according to the California Department of Forestry and Fire Protection.

Officials issued mandatory evacuation orders for a large swath of Ventura County where neighborhoods were being threatened by the blaze, called the Sandy fire. By Monday night, more than 33,000 people in Simi Valley and surrounding communities were under evacuation orders, according to Andrew Dowd, spokesman for the Ventura County Fire Department. Another 10,220 people were under warnings.

Mr. Dowd said on Monday that one home in Simi Valley had burned down, and he spoke by phone as he stood beside it. He said he could see a large plume of smoke nearby as the fire continued to rage and threaten additional structures.

“It’s a huge tragedy to lose one home,” Mr. Dowd said. “We are just in fire-prone territory, and this is a stark reminder.”

The blaze broke out on a warm, breezy day in Simi Valley. The large-scale evacuations were prompted by offshore winds that were fanning the flames.

Investigators were on scene Monday trying to determine the cause of the fire, Mr. Dowd said.

Santa Ana winds from the northeast were blowing at 10 to 20 miles per hour with gusts of up to 35 m.p.h. on Monday morning, according to the National Weather Service, and caused the fire to spread rapidly. By Monday evening, calmer winds and high humidity had significantly decreased the fire’s spread.

Around 750 firefighters remained assigned to battle the blaze on Monday night, along with water-dropping helicopters.

The Sandy fire is burning in the burn scar from the Woolsey fire that grew to nearly 100,000 acres and destroyed 1,643 structures across Ventura and Los Angeles Counties in 2018.

The Woolsey fire eliminated heavy brush that had built up over years, while the Sandy fire is fueled by new growth, particularly dry grasses, said Andy VanSciver, a spokesman for the Ventura County Fire Department.

The fire was burning near several schools in Simi Valley. Officials had canceled outdoor activities and were keeping children inside classrooms because of poor air quality, according to the Simi Valley Unified School District. At least two campuses, Crestview Elementary School and Mountain View Elementary School, had their students and staff evacuated to Simi Valley High School, according to the Ventura County Sheriff’s Office.

The Ronald Reagan Library, on a hilltop in Simi Valley, closed early on Monday because of the fire. The museum isn’t in an evacuation zone but closed “out of an abundance of caution,” said Melissa Giller, a museum spokeswoman.

Ali Watkins contributed reporting.