[Breaking news update, published at 11:17 a.m. ET]

About 23,000 homes -- involving roughly 100,000 people -- have been told to evacuate in the northern Los Angeles area because of the Saddleridge Fire, Los Angeles Police Chief Michel Moore said Friday.

At least 25 homes, many in the Porter Ranch area, have been damaged, Los Angeles Fire Chief Ralph Terrazas said.

Moore again pleaded with people to leave if they're told to do so.

"I saw people firsthand (in evacuation zones) attempting to fight the fire with garden hoses," far outmatched by the flames, he said. "Those individuals placed not only themselves in imminent peril," but also first responders "because of our need and desire to try to rescue them."

Besides burning in northern Los Angeles, the fire also is moving north toward the city of Santa Clarita, Los Angeles County Fire Chief Deputy Dave Richardson said.

Classes in the Santa Clarita area are being canceled, an official said in a news conference.

[Original story, published at 10:30 a.m. ET]

A fast-growing, wind-driven wildfire swept into the northern Los Angeles area overnight, forcing hurried evacuation orders for tens of thousands of people, closing portions of at least three major freeways and sending firefighters scrambling to save homes.

The Saddleridge Fire, which started Thursday and exploded to 4,700 acres by Friday morning, jumped across the 210 and 5 freeways overnight as it spread into northern Los Angeles neighborhoods.

An undetermined number of homes have been destroyed, and mandatory evacuations were called for more than 12,000 homes -- often while occupants were sleeping -- in and near Los Angeles' Porter Ranch and Granada Hills neighborhoods, the Los Angeles Fire Department said.

"When you're told to leave, we mean for you to leave," Los Angeles Police Chief Michel Moore said early Friday. "If you stay in those areas, we cannot guarantee you that we'll be able to find you and rescue you if you're overcome by flames."

Live updates: Fires around northern Los Angeles

This is just one of the several blazes in Southern California fueled by strong Santa Ana winds, with gusts around 60 mph. Many parts of the region are under red-flag warnings -- meaning high fire risk -- into Friday afternoon.

The Saddleridge Fire started around 9 p.m. ET and jumped the 210 and 5 freeways, and some parts those roads and the 405 were closed as orange embers lit up the night sky. By late Thursday it had gutted 60 acres; but some four hours later, it had grown to more than 4,000 acres, fire officials said.

Hector Landeros, who lives in northern Los Angeles' Sylmar neighborhood, said he heard fire trucks and police cruisers speeding through the streets Thursday night as the massive flames got closer.

"In some areas, the streets have started to empty but at the front lines people are watching, waiting on the sidewalk not really knowing what to do," he told CNN early Friday. "There are a lot of people trying to get into their neighborhoods."

Shaun Butch said he saw flames on both sides of the freeway while driving on Interstate 5.

"Everything was engulfed in smoke and visibility was so low it was hard to drive. Everyone on the Interstate 5 north was stopped and trapped. Still was able to barely get through on the Interstate 5 north."

Patsy Zamora said as she drove on the freeway with the fire next to the truck route, she could feel the heat through the windows.

In Sylmar, Mojdan Darabi's husband was spraying their house and yard with a garden hose early Friday, CNN affiliate KABC reported. They both stood outside, anxiously watching flames in the nearby hillsides.

"Yes, I'm worried, but I'm just shooting water everywhere to stop the fire from over here," the husband said.

Cal State Northridge and other schools closed

A number of colleges and other schools have closed Friday because of the fire, including California State University Northridge and Los Angeles Mission College in Sylmar.

The Los Angeles Unified school district closed at least 15 schools and said bus service throughout the district would be delayed.

It's one of multiple fires in the region

The Saddleridge Fire is one of several burning in Southern California.

Another blaze -- the Sandalwood Fire in Calimesa, some 70 miles east of Los Angeles -- has destroyed at least 74 structures since it began Thursday afternoon, according to the Riverside County Fire Department. It has burned at least 500 acres and was at least 10% contained.

It started when the load on a garbage truck caught on fire and spread to vegetation, Capt. Fernando Herrera of Cal Fire Riverside told CNN affiliate KABC.

"Due to the Santa Ana wind influx, obviously this fire just completely went out of control. It started just eating up vegetation as fast as the eye can see," he said.

Residents are under mandatory evacuation orders, and 120 firefighters are assigned to the area.

Less than 20 miles away in Moreno Valley, the Reche Fire has burned at least 350 acres and was 10% contained Thursday evening. The fire went from 100 to 200 acres in about 90 minutes, before nearly doubling two hours later. Mandatory evacuations have been issued in surrounding areas, and the cause is under investigation.

Southern California Edison cut power to almost 24,000 customers Thursday to prevent wildfires caused by high winds downing live power equipment.

In Northern California, utility Pacific Gas & Electric also cut power to hundreds of thousands of customers this week, similarly hoping to prevent wildfires during windy conditions.

CORRECTION: An earlier version of this story misspelled the name of Los Angeles Police Chief Michel Moore, and misidentified the agency he leads.

CNN's Amanda Watts, Chuck Johnston and Stella Chan contributed to this report

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