Seffner, Florida (CNN) -- The ground just swallowed him up.

A Florida man fell into a sinkhole that opened suddenly Thursday night beneath the bedroom of his suburban Tampa home, calling out to his brother for help as he fell, the brother said Friday.

"I heard a loud crash, like a car coming through the house," Jeremy Bush told CNN affiliate WFTS. "I heard my brother screaming and I ran back there and tried going inside his room, but my old lady turned the light on and all I seen was this big hole, a real big hole, and all I saw was his mattress."

Bush frantically tried to rescue his brother, Jeff Bush, by standing in the hole and digging at the rubble with a shovel until police arrived and pulled him out, saying the floor was still collapsing.

"I thought I heard him holler for me to help him," the man tearfully told WFTS.

Jeremy Bush and four other people, including a 2-year-old child, escaped from the blue, one-story 1970s-era home in Seffner, Florida, a Tampa suburb.

Jeff Bush was presumed dead after monitoring equipment lowered by engineers detected no signs of life, said Jessica Damico, the Hillsborough County Fire Department spokeswoman.

But rescuers can't go into the hole to check -- it's too dangerous, Fire Chief Ron Rogers told reporters Friday. Authorities say they worry the hole is still spreading and the house could collapse at any time.

The sinkhole is about 20 feet to 30 feet across and may be 30 feet deep, said Bill Bracken, president of the engineering company assisting emergency workers. The hole was originally reported to be 100 feet across, but that is the diameter of the safety zone surrounding it, Bracken said.

"It started in the bedroom, and it has been expanding outward and it's taking the house with it as it opens up," he said.

Nearby homes have been evacuated as a precaution, Rogers said.

Damico said about 40 police and firefighters were standing by at the scene Friday morning. Meanwhile, engineers with more sophisticated equipment hope to get a three-dimensional image of the sinkhole.

Family members were also on hand, waiting out what they fear will be a devastating day.

"I know in my heart he's dead," Jeremy Bush said. "But I just want to be here for him, because I love him. He was my brother, man."

Sinkholes are common in Florida, according to the Florida Department of Environmental Protection. The state lies on bedrock made of limestone or other carbonate rock that can be eaten away by acidic groundwater, forming voids that collapse when the rock can no longer support the weight of what's above it.

Hillsborough County is part of an area known as "sinkhole alley" that accounts for two-thirds of the sinkhole-related insurance claims in the state, according to a Florida state Senate Insurance and Banking Committee report.Florida Sinkhole Swallows Man