The explosion knocked out the wall of a second-storey unit on Clarence Street at about 6.30am.
NSW Fire and Rescue Superintendent Adam Dewberry said there had been “significant damage”.
“The wall, a double or triple brick wall, has literally blown out of the building off that second level,” Dewberry told Today.
“Now, that explosion also causes a significant pressure wave, which is where the neighbouring properties and buildings have also felt that shockwave.”
Falling rubble destroyed a car parked below.
Firefighters carried one male out of the wreckage, and that person has since been taken to hospital.
“Our focus at the moment is continuing to do a search to make sure we get an all-clear, good, everyone accounted for, which we haven’t got at this stage, but we’re working through it,” Dewberry said.
“But it is still a very precarious and dangerous situation for our firefighters to move in and around.”
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Nearby resident Charlton said he was having “a nice cup of coffee” when the explosion happened.
”And then I heard these two loud bangs, and then I said, ‘my god, it’s like an earthquake going on somewhere’,” he said.
“So I went down and I saw this whole building come down … very scary.”