A man has died from critical burns days after a suspected gas explosion tore through his unit at a retirement home in northern NSW.

A large explosion was reported at the single-level unit on Monarch Dri in Kingscliff about 7.30am on Monday, July 7, with numerous emergency crews responding.

An 85-year-old man was airlifted to Royal Brisbane Hospital in a critical condition with severe burns.

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He has since died from his injuries, police said on Wednesday.

An 83-year-old woman, who was also inside the unit at the time, was taken to Tweed Valley Hospital with burns to her face and body.

She was treated for her injuries and is now in a stable condition.

Fire and Rescue NSW said four fire trucks and 14 firefighters were sent to tackle the blaze, which completely destroyed the unit.

Crews managed to stop the flames from spreading to neighbouring homes.

FRNSW is investigating whether a leaking LPG system may have caused the explosion.

Early advice to police suggests the source may have been a portable gas appliance inside the home.

Investigations continue and a report will be now prepared for the coroner.