A one-story building in a park in Montecito Heights was badly damaged by a fire early Thursday.

The fire at Hermon Park, also known as Arroyo Seco Park, was reported a few minutes after 2:30 a.m.

When firefighters arrived at the scene in the 5600 block of Via Marisol, they found an unoccupied one-story building ablaze.

Firefighters were able to extinguish the flames in about 20 minutes, but not before large portions of the structure collapsed, footage from the scene shows.

The cause of the fire remains under investigation.