Honolulu firefighters are expecting a drawn-out battle to extinguish a slow-moving Makakilo fire accidentally started by two 7-year-old boys.

Honolulu fire Capt. David Jenkins said the upper slope of the fire remained only 20 percent contained Tuesday afternoon and burning deep within thick mats of decaying forest material in extremely steep and rugged terrain.

“It’s not going to be a quick, easy extinguishment,” he said.

The dense forest canopy also protected some smoldering areas from water drops by the fire department’s helicopter, Jenkins said.

He could not estimate when firefighters will extinguish the brush fire, but said operations are expected to be “extended,” judging by past fires with similar circumstances.