A deliberately set fire scorched the business office of Nanakuli High School and several other offices Sunday night, causing more than $400,000 in damage.

Fire investigators and facility inspectors with the state Department of Education are still sifting through the ashes to determine the cause. Initial estimates put damage to the structure at $300,000 and damage to the contents at more than $100,000.

A 59-year-old man called police and firefighters at 10:17 p.m. Sunday night and reported the blaze, which he said he could see from the street nearby.

Shortly before the 911 call reporting the fire, the security alarm system protecting the office went off.

Clayton J. Fujie, deputy superintendent at the DOE, said someone either broke in right before the fire or something was hurled through a window.

He said offices adjacent to the business office, which is in the circle-shaped administration building at Nanakuli High School, sustained some water damage.

"It disrupts (campus life) and unfortunately it's costing taxpayers money," Fujie said.

Honolulu police have opened a first-degree arson investigation into the fire.

No suspects have been identified and police are still looking for witnesses and working with fire investigators.

The blaze spread quickly from the main office to several classrooms. It took firefighters more than 43 minutes to extinguish the flames. An initial investigation revealed the fire was deliberately set.

There were 580 fires classified as arson in Honolulu last year, up from 547 in 2005, 427 in 2004 and 389 in 2003, according to FBI statistics. That's a 49 percent increase over that four-year period.

The fire is the second deliberately set blaze on an O'ahu public school campus this year.

On April 26, fire destroyed a portable classroom at Highlands Intermediate School and caused minor damage to two others. Damage in that fire was estimated at $360,000 to the structure and $25,000 to contents.

Reach Peter Boylan at pboylan@honoluluadvertiser.com.