BERGEN, N.J. –  A New Jersey house where smoke had been reported exploded with volunteer firefighters inside, injuring six of them and sending two to a hospital for treatment of burns, authorities said.

“I thought we were going to have six fatalities, I really did,” said Pompton Lakes Fire Chief Jason Ekkers. “They managed to climb out of the basement with compromised stairs. They all helped each other out, they came out one at a time and we were at the back door, just feeding them out.”

Instead, the firefighters — who fire authorities declined to identify — were doing well Sunday. Four were treated at the scene and two were taken to the hospital with burns and later released.

“We are grateful that they got out of there in time,” said Pompton Lakes Fire Official John Keating. “The men were treated and will need some follow-up because of their burns.”

The homeowner, Tom Garrett, got out before the explosion but lost all of his belongings in the fire. The house was demolished, and the lot is now a charred hull. 

Garrett is temporarily staying with his sister, who lives nearby, Keating said.

The stench of smoke permeated the air in the neighborhood Sunday morning, and  a road was blocked off as emergency vehicles and excavating machines filled it. A cluster of fire officials and personnel from Public Service Electric and Gas investigated the scene.

Keating said it is not yet known what caused the explosion.

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Olivia Alvarez, 17, told NorthJersey.com, part of the USA TODAY Network, that she was looking out the window from her second-floor bedroom across the street when she saw smoke coming from the rear of the home and “thought it was a car or something.” A short time later, she “just saw it all explode,” she said.

“The whole house lifted off the ground, then hit the ground again. The entire house, in one piece,” she said. 

Another neighbor, Shirley Jobes, told NJ Advance Media for NJ.com that she heard the blast and looked out the window to see “pieces of the roof on fire up in the air and falling back down.”

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Contributing: Gene Myers and Steve Janoski, NorthJersey.com; The Associated Press