Three people, amongst them a woman and her one-year-old son, died after a massive explosion rocked a Darling Street block in the Sydney suburb of Rozelle at 4.05am on Thursday.

The blast levelled the building containing an apartment above a convenience store.

The explosion turned the block into a pile of rubble.

Police are believed to be treating the incident that rocked the neighbourhood and could be felt from a kilometre away as an arson attack.

"The blast was pretty close to home," Smeltz said.

"I live just round the corner from the store so I would not be much more than a 100 metres away.

"I have walked past the place almost every day since we moved in.

"Myself, my wife and our two girls were woken up by this massive explosion.

"Nobody really knew what it was.

"I was a bit dazed because I was probably in a deeper sleep than my wife.

"For a moment I thought the roof had been blown off.

"It sounded that close and that loud but it would have been the same for the whole neighbourhood."

Smeltz said he and his wife could see thick black smoke coming from the explosion area and people coming out of their homes to see what had happened.

"We had the kids at home so we did not leave the house," Smeltz said.

"You can imagine the scene that was unfolding.

"I had never been to that particular store but I've had coffees at a coffee shop close by.

"The kids' school is not even a couple of hundred metres up the road as well.

"We just hope that no more bodies are found."