The Keauhou Ranch brush fire was estimated at 51 percent contained Thursday after burning 3,679 acres.
The fire is on the slope of Mauna Loa and mostly within Hawaii Volcanoes National Park.
Jessica Ferracane, park spokeswoman, said almost an inch of rain fell on the area in the afternoon, helping to contain the blaze.
“The last time we had any measurable precipitation in that area is May,” she said.
Ferracane said 93 firefighters were on scene, and another 28 are expected to arrive today from California.
The fire is located about a mile north of Highway 11. Plumes of smoke can be seen from the road.
Ferracane said fire crews have prevented it from reaching the Kipuka Ki Special Ecological Area and reduced its spread toward Volcano Golf Course.
But flames were moving into habitat for the ‘I‘iwi bird, the only such habitat within the park.
Crews are using 5-gallon water backpacks and aerial water drops to battle the flames.
Fire crews are from National Park Service, Hawaii County, state Division of Forestry and Wildlife and volunteers.
The cause of the fire remains under investigation.