CNN  — 

A fire that began overnight in Napa County, California, has rapidly burned 2,500 acres, forcing a local hospital to evacuate on Sunday while authorities placed more than 7,000 people under evacuation notices.

The Glass Fire, which began as a 20-acre brush fire near Deer Park, could spread further by winds that are expected throughout the day, Cal Fire said. The fire is 0% contained.

The fire was reported at 3:50 a.m. PT, Napa County spokeswoman Janet Upton said. The fire is burning near St. Helena, about 25 miles east of Santa Rosa. Cal Fire said the cause is under investigation.

Marin County firefighters battle the Glass Fire on Sunday, September 27, in Calistoga, California.

There are 743 homes and about 1,857 people under a mandatory evacuation order, Upton said, with an additional 2,123 homes and 5,282 people under an evacuation warning, which means they should be prepared to leave if necessary.

More than 2,200 structures are threatened by the Glass Fire as of Sunday night, according to CalFire.

Officials are extremely concerned about winds picking up tonight, Upton said. The National Weather Service has the area along with much of Northern California under a Red Flag Warning for fire danger.

“We don’t want it up there on those ridges when the winds pick up,” Upton said.

St. Helena Hospital was evacuated out of an abundance of caution, the second time the hospital has evacuated this fire season.

Evacuation orders are in place for parts of the surrounding area, and an evacuation center has been opened at the Crosswalk Community Church in Napa, according to the Napa County Office of Emergency Services.

Residents are heeding the warnings, said Napa County Sheriff’s Office spokesman Henry Wofford.

A Marin County firefighter battles the Glass Fire on Sunday, September 27, in Calistoga, California.

“We activated the high-low siren on our vehicles because we knew we needed to get people out of there quickly,” Wofford said. “When they hear that high-low siren coming from cars as we drove through their neighborhoods they know it’s time to evacuate. The motto is, ‘If I can hear it, it’s time to go.’”

Craig Philpott posted photos and videos to his Twitter account that show the Glass Fire blazing red overnight and the fire’s smoke choking the air on Sunday morning.

A new blaze in Northern California named the Zogg Fire has grown to 1,000 acres in just a few hours after it started this afternoon in Shasta County. Mandatory evacuation orders are in effect in some areas, according Cal Fire. Shasta County is northeast of Napa County.

Scope of power shut-offs reduced

The scope of Pacific, Gas & Electric’s power shut-offs to prevent wildfires in Northern California this weekend has decreased from nearly 100,000 customers expected to be affected, to 65,000 customers.

A press release issued by PG&E Sunday attributes the decrease in numbers to “favorable changes in forecast weather conditions.” The utility giant announced the plan late last week due to Red Flag warnings across much of the state.

Power was shut off for 11,000 customers early Sunday morning and the second wave of 54,000 shut-offs is expected to begin at 4 p.m. PT Sunday afternoon, primarily in the Central Sierra Region.

Napa County, where the Glass Fire sparked overnight, is on the list of counties expected to experience shutoffs.

Critical fire weather conditions are in place across much of northern California and portions of Los Angeles and San Bernardino counties. Drought, strong winds, dry vegetation and above-average temperatures are expected across the fire-weary West.

The blaze continues a remarkable wildfire season in the western US that scientists warn is a preview of a new normal as human activity and carbon emissions make the earth hotter and dryer.

Nine months into the year, more than 44,000 fires across the US have burned more than 7.1 million acres, according to the National Interagency Fire Center. That’s already 1 million more burned acres than the yearly average over the last 10 years. An average of 46,409 fires are reported each year.

In California, five of the state’s top 10 largest fires in recorded history, in terms of acreage, have occurred in 2020 and are still burning.

CNN’s Haley Brink, Allison Chinchar and Jenn Selva contributed to this report.