Dunedin Deputy Fire Chief Trip Barrs said the hole appeared to be about 12 feet wide when officials arrived on the scene. Residents of the neighboring houses also were evacuated as a precaution.
The Tampa Bay Times reports that the ground is so unstable that two homes must be demolished.
Television footage showed part of a patio caved in and a boat on the edge of the hole. Tampa area television stations reported that a neighboring pool appears to have cracks.
The affected neighborhood is in Dunedin, a small city in northern Pinellas County, about 20 miles north of St. Petersburg.
Sinkholes are common in Florida because the peninsula is made up of porous carbonate rocks such as limestone that store and help move water underground. Over time, the rocks can dissolve from an acid created from oxygen in water, causing a void under the limestone roof. When dirt, clay or sand gets too heavy for the limestone roof, it can collapse, creating a sinkhole.
On Feb. 28, Jeffrey Bush died when a sinkhole opened under his bedroom in Seffner, Fla., near Tampa. His body was never recovered. In August, sections of a building at a resort near Orlando collapsed into a sinkhole. No one was injured.
Homeowner Michael Dupre said the family heard a noise that sounded like a sledgehammer pounding on the wall early Thursday morning.
Dupre told Bay News 9 there had been "sinkhole activity" in the area. "After the Seffner sinkhole, we were scared. We've been dealing with our insurance company and finally two days ago, they started working on our house. Now it looks like our house is gone."
As the hole grew, it swallowed the Dupre's porch and new boat. Now, his neighbor's swimming pool and a portion of that home have fallen in as well.
Engineers were called in to assess the homes and ultimately decided both Dupre's home and his neighbor's would be complete losses.
A backhoe was used to pull Dupre's boat from the hole. Crews had feared fuel in the boat could leak into groundwater. Otherwise, the rescue crews are in a holding pattern until the hole stabilizes.
State officials say three counties in the Tampa region are known as "sinkhole alley." Two-thirds of the sinkhole damage claims reported to the state Office of Insurance Regulation between 2006 and 2010 came from Hernando, Hillsborough and Pasco counties. Dunedin is in neighboring Pinellas County.