Honolulu Fire Department officials said they believe 7-year-old twin boys started a fire in Makakilo.
Palehua Road reopened to residents shortly after 12:30 p.m. Sunday. Fire officials estimate flames damaged more than 800 acres.
Officials are still on the scene working to contain the fire.
Officials said the boys found lighters and played with them in the gulch area at the top of Kikaha Street.
Officials said about 60 firefighters were working to contain the fire. They said they were also working to protect communication towers at the top of the ridge.
Firefighters said their focus was on about 20 homes on Palehua Road. Four helicopters were dumping water onto the fire.
The federal fire department was assisting with the containment efforts. Officials said the fire is going uphill in the wind, which is difficult to fight.
No injuries or structure damage have been reported.