City, federal and Army firefighters had a three-and-a-half acre wildfire 90 percent contained at 5 p.m. Thursday in the Army’s Kahuku Training Area about 1 to 2 miles above Kamehameha Highway.

Crews were expected to continue to battle the blaze until dark at about 7:30 p.m. Thursday.

The cause of the fire remains unknown, Honolulu Fire Department Capt. Terry Seelig said in a news release.

The fire burned grass, brush and trees in the Koolau Mountains, but did not cause injury or damage property or equipment, the Fire Department reported.

Strong winds, difficult access and water supply challenged firefighters, who used hand toools and hose lines from pumpers to control the fire. Water tankers shuttled water to the pumpers.

Winds were blowing at about 20 knots, and firefighters traveled over steep narrow roads for about 4 miles to reach the fire, Seelig said.

The Fire Department was called to the scene at 2:33 p.m. Five engines, three water tankers, a helicopter and a fuel tender responded.

The Federal Fire Department was using two engines, a brush truck and a water tanker, and Army Fire’s brush truck was used.