Emergency services were called to a home on Dora Street in Hurstville just before 9am following reports of the explosion, which has left the man with burns to 70 per cent of his body.

Officials are investigating whether nitrous oxide, also known as laughing gas, was the cause of the explosion.

Multiple cylinders of the gas were found at the property.

Specialist doctors were among the first responders at the scene.

A 39-year-old woman was also injured, suffering serious burns.

She was taken to Concord Hospital in a serious condition. 

The 30-year-old man was taken to Royal North Shore Hospital in a critical condition with burns to his airways. 

Paramedics “put the patient in an induced coma and intubated the patient on the scene,” NSW Ambulance Inspector Dominic Wong said.

“That’s to make sure we protect the patient from further deterioration.”

Police have sealed off the home, declaring it a crime scene.

Investigators are looking into the exact circumstances of the explosion.