A massive brush fire on the upper slopes of the windward side of the Waia­nae Mountains ridge has burned 1,000 acres and is slowly being pushed by winds uphill toward a forest reserve that is home to 90 rare and endangered plant and animal species.

The fire was accidentally set by twin 7-year-old brothers Friday playing with a lighter.

Capt. David Jenkins, a Fire Department spokesman, said the fire along the lower slope near Umena Street and Palehua Road has been completely contained. Parts of the fire along the upper slopes and heavily forested areas were 20 percent contained. Firefighters are trying to prevent the fire from entering a deep gully.

Jenkins said that flare-ups occurred in the Palehua area on Monday but were quickly brought back under control by fire crews.

The massive brush fire is threatening 90 rare and endangered plant and animal species in the Honouliuli Forest Reserve, according to the state Department of Land and Natural Resources. The endangered Oahu elepaio bird and endangered "singing" kahuli tree snail also live there.

Jenkins said that while the reserve is in an area inaccessible to firefighters, moist conditions have slowed the fire’s advance.

"It’s more of a smoldering type of fire there," Jenkins said. "It’s going to take a while. It probably won’t be fully extinguished until the rainy season."

Nine fire companies, involving 20 firefighters, were on site on Monday to battle the blaze.

They were without the service of the fire department’s Air 1 helicopter, which was under repair.

The fire prompted the evacuation of about 20 houses on and near Umena Street in Makakilo and 20 cabins and other structures at Camp Timberline when it broke out on Friday.

One home sustained minor structural damage. The flames scorched a wall and door of one home.