Investigators are working to figure out what caused a large fire to break out Tuesday afternoon at a CVS in St. Pete Beach — and reignite later that night, with flames spreading to the adjacent Publix. Pinellas County Emergency Services received a call just after 2:45 p.m. about a structure fire at 4685 Gulf Boulevard. At least 42 fire units were sent to the three-alarm blaze. Marc Portugal, a spokesperson for St. Pete Beach, said crews believe the fire started inside the CVS. Cameras showed a large plume of smoke billowing from the store, which is located in the Dolphin Village Shopping Center along with a Publix, UPS Store, Swim City, Verizon, Playa Bowls and Zenshi Sushi. Aerial footage from Sky 10 also showed the roof of the CVS charred and disintegrated. The city of St. Pete Beach confirmed that there was a "partial roof collapse," and the building was left with "extensive damage." Officials said surrounding businesses were evacuated. “We heard the people yelling and then saw the white smoke coming out from over this area and then the black smoke followed behind it,” one witness said. That’s when people started running out “frantically screaming,” another witness added. Just before 6:30 p.m., the city of St. Pete Beach said the fire was out. While fire crews said the flames were initially contained to the CVS, the blaze flared back up on Tuesday night, spreading to the Publix in the plaza. Parts of the front facade of the Publix burned down to the studs, with large chunks of the building crumbling to the ground. "During overhaul operations, additional hot spot fires ignited in void spaces within the building's front façade, where there were no clear access points. Fire crews were forced to breach the structure’s exterior using hose line pressure to reach and extinguish the flames. The fire spread across the façade to adjacent businesses south of CVS within the plaza, resulting in smoke and water damage to multiple units," the city of St. Pete Beach said in a Wednesday morning update. Officials say the fire was fully extinguished and contained at around 11:30 p.m. Gulf Boulevard was closed Tuesday as crews worked to get the fire under control, but it has since reopened. All businesses in the CVS and Publix complex will remain closed Wednesday as a precaution and safety measure.