Dad and son killed by 'campsite fridge gas leak' in WA beach holiday tragedy

A father and son have been killed in their sleep along with the family dog, apparently poisoned by gas leaking from a refrigerator in a holiday campsite tragedy in Western Australia.

Police said they were called to reports of a child who was not breathing at Dide Beach, north of Perth, at 10.50am on Monday, and found a man aged in his 40s and his 11-year-old son dead.

A woman - the man's wife and the child's mother - also needed urgent medical help.

Police believe the two victims were killed, along with the family's pet dog, during their sleep on the campsite after a poisonous chemical leaked from a fridge inside their tent.

The woman had been laying next to the pair but survived.

She was flown to the Fiona Stanley Hospital for exposure to the gas as well as signs of hypothermia.

9News understands two other families had been staying with them on the holiday and raised the alert to authorities after the dad and son were unable to be woken in the morning.

The couple's two other children had stayed at home in Perth while the others were away camping.

An emotional family friend and witness, Roslyn Smith, told 9News the first concern was the welfare of the two other children.

"That's their main worry - was getting in touch with the two that were at home," she said.

"We're just talking to them and trying to calm them down."

The mother remains in hospital in a stable condition and has regained consciousness.

Crews from the Department of Fire and Emergency Services and WA Police also attended the scene again today to remove the equipment and clear the family's belongings which had been left behind, including their car.

Authorities want to speak to anybody who was camping in the area.A report will be prepared for the Coroner.