Gas leak probed as cause of deadly Sydney blast

Gas experts will investigate the confronting scene of a blast that collapsed a Sydney unit complex after the body of a woman was found in the rubble.

The victim, aged in her 30s, was found by emergency workers about 3.20am on Monday, after the explosion levelled the two-storey property in the suburb of Whalan on Saturday afternoon.

It's speculated that a gas leak played a role in the deadly blast amid reports locals smelled gas in the area in recent weeks.

"There was always a gas smell ... like a leak," Andrew, whose grandfather lives in the complex, told 9 News.

Another neighbour said she felt unsafe and worried her home might also be affected.

Five other people were hospitalised following to the explosion, which was felt across several suburbs in the city's west.

Blacktown Detective Superintendent Darren Newman said independent experts would attend the site to "get the best information available as to how this occurred".

"They'll go through a whole process and they'll work with our crime scene examiners to make sure that we can thoroughly investigate this," Supt Newman told reporters in Whalan.

The woman's body was located after a crane was used to move the property's concrete slab, dashing hopes she would be found alive.

Choking back tears, Supt Newman said the victim's mother was devastated by the loss and that police had been working with her since the collapse.

"Obviously we had to deliver a death message this morning," he said, describing the incident as difficult and confronting for emergency workers.

"We just do the best we possibly can."

The police investigation will be a part of a report for the coroner, who had been on site with emergency teams on Monday, authorities said.

While the cause of the explosion is unknown, NSW Deputy Premier Prue Car has said she is "deeply concerned" amid reports gas could be a factor.

NSW Fire and Rescue Commissioner Jeremy Fewtrell previously said there had been a leak at the site after the explosion, which hampered rescue efforts.

Dozens of search and rescue technicians, including firefighters who responded to last year's Turkey earthquake disaster, had been working at the scene.