Engineers were working carefully today to find out more about a slowly growing sinkhole that swallowed a Florida man in his bedroom, believing the entire house could eventually succumb to the unstable ground.

Jeff Bush, 37, was in his bedroom on Thursday night when the earth opened and took him and everything else in his room. Five other people were in the house but managed to escape unharmed.

Mr Bush's brother jumped into the hole to try to help, but he had to be rescued himself by a sheriff's deputy.

Engineers began doing more tests at 7am local time today. Crews with equipment were at the home next door, one of two that have been evacuated.

By 10am, officials moved media crews further away from the Bush house so experts could perform tests on the home across the street. It was unclear how large the sinkhole is, or whether it leads to other caverns and chasms throughout the neighbourhood. Experts say the underground of West Central Florida looks similar to Swiss cheese, with the geography lending itself to sinkholes.

Experts spent the previous day at the property, taking soil samples and running various tests - while acknowledging that the entire lot where Mr Bush lay entombed was dangerous. No-one was allowed in the house.

"I cannot tell you why it has not collapsed yet," Bill Bracken, the owner of an engineering company called to assess the sinkhole, said of the home. He described the earth below as a "very large, very fluid mass".

"This is not your typical sinkhole," said Hillsborough County administrator Mike Merrill. "This is a chasm. For that reason, we're being very deliberate."

Officials delicately addressed another sad reality: Mr Bush is probably dead and his family want his body. Mr Merrill said, however, that they do not want to jeopardise any more lives. "They would like us to go in quickly and locate Mr Bush," he said.

Officials said today that a fund had been set up to help families affected by the sinkhole.

Today, Jeremy Bush - who tried to rescue his brother when the earth opened up - lay flowers and a stuffed lamb near the house and wept.

Hillsborough County Fire Chief Ron Roger called the situation "very complex".

"It's continuing to evolve, and the ground is continuing to collapse," he said.

Sinkholes are so common in Florida that state law requires home insurers to provide coverage against the danger. While some cars, homes and other buildings have been devoured, it is extremely rare for them to swallow a person.

Florida is highly prone to sinkholes because there are caverns below ground of limestone, a porous rock that easily dissolves in water.

"You can almost envision a piece of Swiss cheese," said Taylor Yarkosky, a sinkhole expert from Brooksville, Florida, while gesturing to the ground and the sky blue home where the earth opened in Seffner. "Any house in Florida could be in that same situation."

A sinkhole near Orlando in 1981 grew to 400ft (122m) across and devoured five sports cars, most of two businesses, a three-bedroom house and the deep end of an Olympic-size swimming pool.

More than 500 sinkholes have been reported in Hillsborough County alone since the government started keeping track in 1954, according to the state's environmental agency.

The latest sinkhole, estimated at 20ft (6m) across and 20ft (6m) deep, caused the home's concrete floor to cave in around 11pm on Thursday as everyone in the Tampa-area house was turning in for the night. It gave way with a loud crash that sounded like a car hitting the house and brought Mr Bush's brother running.

Jeremy Bush said he jumped into the hole but could not see his brother and had to be rescued himself by a sheriff's deputy who reached out and pulled him to safety as the ground crumbled around him.

"The floor was still giving in and the dirt was still going down, but I didn't care. I wanted to save my brother," he said through tears yesterday. "But I just couldn't do nothing."

He added: "I could swear I heard him hollering my name to help him."

A dresser and the TV set had vanished down the hole, along with most of Mr Bush's bed.

A sheriff's deputy who was the first to respond to a frantic emergency call said that when he arrived he saw Jeremy Bush.

Deputy Douglas Duvall said he reached down as if he was "sticking his hand into the floor" to help Jeremy Bush. Mr Duvall said he did not see anyone else in the hole.

As he pulled Mr Bush out "everything was sinking", Mr Duvall said.

Engineers said they may have to demolish the small house, even though from the outside there appeared to be nothing wrong with the four-bedroom, concrete-wall structure, built in 1974.

Jeremy Bush said someone visited the home a couple of months ago to check for sinkholes and other things, apparently for insurance purposes.

"He said there was nothing wrong with the house. Nothing. And a couple of months later, my brother dies. In a sinkhole," he said.

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