MAYWOOD — A three-alarm fire ripped through a pair of commercial buildings in Maywood today, sparking a series of strong explosions, knocking out power and forcing the evacuation of about 200 residents and nearby workers while sending a thick plume of potentially toxic smoke over the region.

• PHOTOS: See the Maywood magnesium fire that is spreading odors across Southern California

The blaze in the 3700 block of Fruitland Avenue just a few miles east of the Long Beach (710) Freeway was reported at 2:30 a.m. in a warehouse serves Gemini Plastic Enterprises, according to the Los Angeles County Fire Department.

• VIDEO: See HUGE explosion at Maywood warehouse fire

County Fire Chief Daryl Osby said arriving crews found flames shooting through the roofs of two structures, one of which was a metal-recycling plant. Crews began pouring water on the flames, but the oxygen from the water created a chemical reaction with the burning metals, producing what one fire official described as “fireballs” that set off strong explosions.

“We had some very violent, ferocious explosions in the facility,” Osby said. “We have several unknown products that are burning, and we have a cadre of exotic metals — magnesium, coppers, zinc, lead — that are yet to be determined, along with chemicals and propane.”

Osby said fire crews quickly went into a defense mode, and no injuries have been reported. He said crews were able to prevent the blaze from spreading to other businesses and nearby homes, but the two commercial structures were destroyed.

The Los Angeles County Sheriff’s Department deployed deputies from several sheriff’s stations to the area, and about 200 residents were evacuated from homes and businesses as a precaution while authorities assessed air quality. Traffic was routed away from the area.

“The majority of the evacuations were mandatory (and) other residents voluntarily evacuated to safety,” according to the sheriff’s department.

A shelter was set up for evacuees at the Maywood YMCA at 4801 58th St.

The blaze led more than 3,100 customers in the area to lose power at 2:45 a.m., and crews were sent to handle the problem, a Southern California Edison representative said.

A hazardous-materials team was sent to the scene, and officials from the South Coast Air Quality Management District were notified.

The AQMD later issued a smoke advisory, saying odor from the plume of smoke was prompting complaints across the region.

Los Angeles Fire Department spokesman Brian Humphrey said reports of an acrid smell were coming in to authorities from all areas of the city.

Humphrey urged residents not to call 911 to report the acrid smell, and to limit such calls to situations in which people see smoke or flames from an active fire, or if they have a medical emergency.

AQMD officials said experts are taking measurements to assess possible toxic concerns. Residents were advised to avoid vigorous outdoor exercise in areas affected by the smoke, particularly in central, south-central and southeastern parts of the county. People with heart or respiratory disease, children and older adults were advised to remain indoors.