Firefighters moved into defensive positions as the fire burned out of control on Figueroa Street near Rosecrans Avenue and the 110 Freeway.
AIR7 video shows crews throwing water on the fire from the roof of a nearby business as thick black smoke filled the air. The Los Angeles Fire Department said crews were using ladder pipes and heavy streams.
The building is 1,000-square feet and appeared to be burning quickly.
LAFD said 78 firefighters were working to extinguish the flames.
In a later update, the department said crews were preparing to make entry into the building for final extinguishment.
The Harbor Gateway was one of several fires that burned throughout the region on the Fourth of July.
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Massive blaze tears through La Habra commercial building
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