LARGO, Fla. — Investigators are working to find out what caused the massive fire at a former grocery store in Largo Saturday.

The store is the former Winn-Dixie on Seminole Boulevard. It's a 42,000-square-foot store.

When firefighters got to the plaza there were flames and heavy smoke. Within 10 minutes of going into the building they had to evacuate because pieces of the roof were calling off.

"Initial report was fire started in the front left corner of the structure in the kitchen area," said Largo Fire Marshal Don Rooks. "Had some ceiling cut loose, made it up into the attic space, ran the attic, then the AC unit dropped. Went defensive. So we have nobody inside."

Pinellas County says about 68 firefighters were needed to put out the fire from above and below. 

At least one business nearby was evacuated, but the owners say there was no damage.