An autopsy has confirmed that two boys in Eastern Canada who were apparently attacked in their sleep by a four-metre python died of asphyxiation, police in New Brunswick said.

Noah and Connor Barthe, aged four and six, were found dead early on Monday after the snake, a 45-kg African rock python, escaped from its glassed-in enclosure, slithered through a ventilation shaft and fell into the room where they were sleeping.

A necropsy was performed on the snake, which was euthanized after the attack, and police said it appeared to be in good health.

The boys were at a sleepover in an apartment above the Reptile Ocean exotic pet store in Campbellton, New Brunswick, a town of about 7,500. The snake was being held in a glass enclosure in the same apartment.

The deaths dominated headlines in Canada and prompted questions about the safety and legality of keeping exotic pets in private residences.

The government of New Brunswick has said African rock pythons cannot be kept within the province without a permit, which would only be granted for an accredited zoo, not a private residence.