Fire officials believe a leak in a liquid petroleum gas tank line may be responsible for the explosion that reduced a three-story, 5,000-square-foot home on Lake Lanier to a pile of rubble.

Homeowners Dan and Susan Johnson and their adult son, Michael Allen Clack, were home when the blast shook the upscale Blackberry Lane house around 5:30 a.m. Friday.

All three were transported for medical treatment, but a family member confirmed that everyone will be OK.

Neighbor Nancy Karr spent Friday morning carefully stepping through her yard, avoiding the mixture of broken glass and the family's personal items fanning out from the property in all directions.

She fished a baby picture from her koi pond and began taking pictures of the LP gas tank believed to be at the center of the destruction.

"The noise — I've never heard a noise like that. One big boom," she said. "I grabbed my husband and started screaming. I thought, ‘Oh my God, the end of the world is coming.'"

Another neighbor, Jim Wingo, said he was the first on the scene after the explosion blew open several of his doors in the middle of the night.

"I could hear (Clack) over there calling for help," he said.

"He was lying on his side and had a piece of interior wall on him. I was able to lift that up enough for him to pull himself out."

However, Wingo said the Johnsons, who slept on the middle floor, were trapped in the house. He could hear Dan Johnson yelling beneath the rubble, but wasn't able to get to them.

"(Clack) wanted to help his mom and step-dad," he said.

"I told him there wasn't much I could do.

"I couldn't see them. They were completely covered with debris but the father could see my flashlight shining. I could hear him but I couldn't understand what he was saying. ... I couldn't hear the mother, but Dan said he could hear her and was talking to her."

Emergency crews responded at 5:58 a.m. and began using chain saws to dig the couple out, according to Capt. Scott Cagle, Hall County fire marshal.

Neighbors say both Dan and Susan Johnson sustained broken bones but were conscious when they were freed about half an hour later.

Clack, who lived in the basement, suffered "flash burns," Cagle said.

Fire investigators stood around a 120-gallon LP gas tank as they began sifting through the rubble Friday afternoon.

Though Cagle said it's too early to point to a cause, it appears the house filled with gas before igniting.

When firefighters originally arrived, Cagle said the LP tank was leaking.

"(It) can still be intact if there was a leak in the line," he said.

"So if there was a leak in the line and all the gas leaked into the house, any ignition source could have done it. A telephone, AC unit kicking on, a ceiling fan, something like that. It's common for the tank to still look like it's OK."

The explosion rippled out across the neighborhood and was heard miles away.

Next-door neighbor Jim Karr said it shifted his entire house a couple inches and broke several windows.

A 4-foot tall wooden totem pole which used to sit inside the home's entrance, was found by the lake more than 100 yards away.

"The house was very well insulated so it was pretty much a pressure cooker in there before whatever ignition source it was exploded it," Cagle said.

The family continues to look for three missing dogs.