(CNN) A sinkhole in Florida that swallowed two houses appears to have stopped expanding, meaning a recovery-and-repair operation can begin, authorities said.

Five homes in Land O' Lakes, a residential area about 20 miles north of Tampa, are unsafe for entry, officials said Saturday. Residents of four dwellings were allowed to return.

It's the largest sinkhole in Pasco County in at least three decades.

No injuries were reported. Officials said it will take weeks, perhaps months, for life to fully return to normal for residents in the neighborhood.

The sinkhole, estimated to be 225 feet in diameter and 50 feet deep, apparently began beneath a boat, which fell into the widening depression.

The active sinkhole is full of water and not draining because of debris, said Kevin Guthrie, Pasco County's assistant administrator for public safety. It also looks like it's full of household chemicals and septic tank parts.

"We're treating this, in essence, as a hazmat incident," he said.

"It is probably a good thing that this sinkhole has actually been stopped up," he told reporters on Saturday. "There are a lot of contaminants in this water. It will allow us to decontaminate the area ... and clear the debris out."

A house starts falling Friday into a sinkhole in Land O' Lakes, Florida.

Fast-moving sinkhole

Authorities were called Friday morning about a depression the size of a small pool.

Pasco County Sheriff's Deputy Jason Murphy said he arrived at 7:48 a.m. ET to find that a sinkhole had reached the corner of one house. Nobody was home, he said, but fire and rescue personnel were able to get two dogs out before a corner of the house fell into the sinkhole.

By that point, the sinkhole was growing quickly, with "large chunks of the ground actually caving in," he said.

Murphy went to the second house and helped an elderly woman and two other females get out, he said. Other deputies yelled for them to move quickly because the ground was collapsing underneath a corner of the house, he said.

The residents of the first house drove up in time to see the rest of their house destroyed, Murphy said, speaking to reporters in front of the sinkholes.

"As soon as they got here, what you see now is what they witnessed as the house caved into the hole," the deputy said. "They were unable to get any belongings. Everything they owned was in there."

It may be weeks before streets near the sinkhole reopen, Land O' Lakes officials said.

Murphy and a resident of the second house managed to get back inside to retrieve medications and documents before the final collapse, he said.

The sinkhole, Murphy said, expanded quickly.

"You're looking at about half an hour in time from (being) only a couple of feet across to taking up their entire yard to taking in part of the house and reaching over into the next house," he said.

The sinkhole grew 25 feet to 30 feet per hour at first, then slowed to 10 feet per hour, Guthrie said.

People who live in some other houses at risk have removed some possessions and pets.

Sinkhole site spurs septic concerns

Authorities have not said what caused this sinkhole. Pasco County records show the houses were built on the site of a sinkhole, Guthrie said.

Sinkholes often form when acidic rainwater dissolves limestone or similar rock beneath the soil, leaving a large void that collapses when it's no longer able to support the weight of what's above it, whether an open field, a road or a house.

Sinkholes are particularly common in Florida, which rests on a nearly unbroken bed of limestone, according to the Florida Sinkhole Research Institute. They often develop in Central Florida, including the Tampa area.

A sinkhole in Land O' Lakes, Florida, swallowed two homes and forced the evacuation of nine others.

Deputies will be stationed in the neighborhood to protect residents and notify them of any problems, Sheriff Chris Nocco said Friday.

"For citizens, our hearts break for you," he said. "We know there's a high level of anxiety. ... I know it's going to be very hard for you to sleep tonight. Any bump in the night, you're going to wonder what's going on with your house."

People were urged to stay away from the neighborhood. A fence will be built around the affected houses, and roads will be closed, Nocco said.