Emergency services were called to Waikanda Cres in Whalan shortly before 1pm on Saturday following reports the second level of the building had “blown out”.

In total, five people were evacuated from the building, including a wheelchair-bound woman in her 60s and another woman aged in her 70s from the property.

Drone images released by Fire and Rescue NSW on Saturday evening captured the devastating extent of the blast, which severely damaged neighbouring units.

Dozens of rescuers were continuing to comb through the rubble as the sun set and rains worsened following reports one person was still missing after the blast.

In a statement, Fire and Rescue NSW said firefighters were using seismic monitoring equipment to “capture any sounds under the ruins”.

It came amid reports of a tapping sound heard underneath the rubble as a large-scale search got underway on Saturday afternoon.

Rescuers were initially prevented from entering the units because of a large gas leak that was unable to be shut off.

Once isolated, fire fighters were able to step up their search and clear the rubble and were using concrete-cutters to clear the debris.

In doing so, rescuers were also able to retrieve a small dog from the ruins of the home, which was then taken care of at the scene.

A NSW Ambulance spokesperson earlier said at least two people were taken to Mt Druitt Hospital in an unknown condition after the blast.

A further two patients were believed to have also been taken to the western Sydney hospital, but had not yet been confirmed.

In a statement, NSW Police said officers were assisting at the scene and that an investigation would be launched into the explosion.

“An investigation into the circumstances surrounding the explosion has commenced.” the statement said.

“Localised traffic diversions are in place. Residents and motorists are urged to avoid the area”.

FRNSW earlier said the “large blast” had blown out windows and damaged neighbouring townhouses in the multi-unit complex.

“The gas company has been unable to cut off supply to the scene and is attempting to isolate the mains,” the statement said.

“There is no fire at present but the scene remains volatile and unstable.

“The public is urged to stay away from the scene while emergency operations continue.”

More than a dozen FRNSW appliances were still at the scene alongside ambulance crews, including rescue teams, hazmat crews, and ladder appliances.

Firefighters had also dispatched remotely controlled drones to make an aerial assessment of the blast zone.

Locals took to social media following reports of a loud bang in the area.

“I was in my front yard In Lethbridge Park and felt and heard this,” one local said.

Others said they felt the explosion as far away as Emerton and St Clair.