An underground mulch fire burned more than an acre of a wooded area in Brentwood on Saturday night before firefighters could extinguish it, authorities said.

The fire began at around 8:30 p.m. in the Bishop Preserve, near Stein Drive and Oakwood Avenue, according to the Brentwood Fire Department.

The department received a call reporting smoke in the area and found a "significant brush fire" burning, along with several spot fires, according to a statement issued by the department.

It took seven hours and more than 100 firefighters to battle the fire, and included assistance from the Suffolk County police, which sent an aviation unit to help determine the extent of the fire, which was burning under mulch piles, the fire department said.

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Bulldozers and heavy equipment had to be used to dig into the mulch and the earth under it to fight the fire, according to the department. The effort took about seven hours as firefighters made sure all the embers were out.

Five departments responded, and no firefighters were injured. No structures were damaged.

The Suffolk County Fire Marshal's office was investigating, according to the fire department.

Suffolk police said its arson squad was notified of the fire, but is not investigating.