By Alex Dobuzinskis

LOS ANGELES (Reuters) - Cooler weather helped firefighters make significant gains on Saturday against a massive wildfire in Southern California, as crews cut containment lines around nearly 50 percent of the blaze.

The so-called Mountain Fire has burned across more than 27,000 acres of dry brush and timber and destroyed seven residences since it broke out on Monday. At least 5,600 residents remain under evacuation orders.

The more than 3,000 firefighters tackling the blaze on Saturday managed to expand containment lines to encircle 49 percent of the fire, up from 25 percent earlier in the day, said Carol Jandrall, fire information officer for the multiagency team battling the conflagration.

"It's been probably the best day so far," she said of the progress made on Saturday.

Higher humidity and clouds, which reduced sunlight on the burn area and tempered the intensity of the flames, helped firefighters cut more containment lines along the east and south flanks of the fire where it originated, Jandrall said.

Firefighters had hoped for rain, but little precipitation actually fell, she said. At the same time, the erratic winds that can propel a fire and had been feared as the weather changed also did not materialize, Jandrall said.

The flames have forced the evacuation of the town of Idyllwild, a community about a mile above sea level known for its hiking trails, rock climbing, and arts and music scene, and also forced out residents from the nearby community of Fern Valley.

Residents of Idyllwild and Fern Valley have been out of their homes since evacuations were ordered on Wednesday.

A few hundred people have been allowed to return home in neighboring areas where the threat of flames has decreased, said Norma Bailey, a spokeswoman for the team combating the blaze.

The Mountain Fire is 90 miles east of Los Angeles.

Conditions could improve on Sunday, Jandrall said.

"They are expecting a chance for more precipitation which would be great," she said.

(Reporting by Alex Dobuzinskis; Editing by Dan Whitcomb, David Brunnstrom and Eric Beech)