The fire at the Americas Best Value Inn, at 23150 Lake Center Drive, was reported just before 8 a.m. Sunday, said Kris Concepcion of the Orange County Fire Authority.
About 100 firefighters battled the six-alarm fire at the three-story, four-building motel. Twelve engines and four trucks battled flames up to 30 feet that broke through the roof, but no major injuries were reported and the fire was under control within three hours, Concepcion said.
One firefighter was treated for heat exhaustion.
The Marines, who happened to be staying at the hotel, helped evacuate some guests even before firefighters arrived.
Residents said the Marines went room-to-room, banging on windows and doors, dodging the flames and yelling at guests to get out and helping some collect their belongings, the Orange County Register reported.
Amy Amadito-Phelps, who was in a room on the second-floor, told the newspaper that she and her husband and 14-month-old son might have died if not for the Marines.
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"We were right next to a room completely on fire and we couldn't smell smoke," she said. "No fire alarms were going off. The only thing we heard was Marines banging on our windows and telling us to get out."
Marine Pvt. Colton Oliver told the newspaper that he and two other Marines were on a second-story landing about 8 a.m. when they saw flames coming from behind a soda machine and smoke billowing out of some of the rooms.
Oliver, Pvt. Josh Hernandez and Pvt. 1st Class Thomas O'Brien knocked on doors and windows to make sure everybody got out, and the other Marines helped.
Hernandez carried one older man out and ran under the flames to help residents, the newspaper reported. After the fire he was treated with oxygen.
"Everybody was out by the time the firefighters got here," Oliver told the Register. "It's what we're trained to do."
Kenneth Evans, who was also on the second floor, told the newspaper that the Marines saved his life.
"The fire was blazing and smoking, but they kept yelling that there was a fire and got everybody out," he said. "I'd probably be dead now if not for them."
OCFA Capt. Steve Pardi told the newspaper that the six Marines were the first responders.
"I'd call them absolute heroes," he said.
A damage estimate was not immediately available, although Concepcion said two of the four buildings in the complex were "probably total losses."
The cause of the fire, which displaced 100 to 150 people, was under investigation.
Amadito-Phelps said she and her family had been staying at the motel for two months after being evicted from their Lake Forest apartment because her husband's job wasn't paying enough.
"My wallet, my laptop, baby stuff, everything is in there," she said. "Everything is gone."