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SAN DIEGO — Crews battled a fire in the South Bay that had grown to 28 acres late Saturday morning. Firefighters began containing the fire within a matter of hours and announced it had been 100% contained by Sunday evening.

Cal Fire San Diego started fighting the flames in a brush-filled area of the Lower Otay Reservoir, near the border east of Chula Vista, around 10 a.m.

The fire grew from five acres to 10 in about 30 minutes and was up to 28 acres after 11 a.m., Cal Fire said. Crews were making progress and the blaze was 5% contained, according to the agency. By 5 p.m., the fire was 50% contained and had not grown.

Cal Fire did not say any buildings were threatened by the flames. Both air and ground units were dousing the fire.

“Total of 11 engines, four fire crews, one bulldozer, three helicopters, two air tankers,” Cal Fire Battalion Chief Patrick Walker said. “Pretty remote area access is an ongoing challenge. We do have resources that made it into the fire now through the access roads. We also have a Cal Fire dozer helping to improve some of the access roads in there.”

Walker said crews would remain at the scene throughout the evening to mop up and ensure there were no further flare-ups.

The cause of the fire was under investigation.