Firefighters have contained 90 percent of a brush fire that has consumed an estimated 5,800 acres in the West Maui mountains since Monday, a county spokeswoman said.

But the fire flared up at about 1:30 p.m. yesterday on the Waikapu side of the perimeter, said Mahina Martin. The flare-up was about a quarter-mile above the Kamehameha Golf Course clubhouse but was moving mauka and did not pose an immediate threat to structures.

Both lanes of Maui’s Honoapiilani Highway remained open today as fire officials extinguished hot spots, assisted by water drops from the Fire Department helicopter. Two helicopters dropped water on the flare-up. State firefighters from the Division of Forestry and Wildlife were working on the mauka perimeter of the fire.

The cause is under investigation.