A python that escaped from a pet shop has killed two children by asphyxiating them in their sleep in eastern Canada.

The two boys - named locally as Noah Barthe, 5, and his brother Connor, 7 - were at a sleepover at their best friend's flat in the town of Campbellton when they were attacked by the snake.

The animal had escaped from the Reptile Ocean pet shop run by family friend Jean-Claude Savoie, located on the ground floor of the building. The shop specialises in exotic pets.

Police said the African rock python entered the upstairs apartment via the two-storey building's ventilation system. The boys were sleeping in the living room when they were attacked by the snake early on Monday morning.

"The preliminary investigation has led police to believe that a large exotic snake had escaped its enclosure at the store," the Royal Canadian Mounted Police said in a statement.

"(It) got into the ventilation system, then into the upstairs apartment. It's believed the two boys were strangled by the snake."

The boys' mother, Mandy Trecartin, lives close to the Reptile Ocean store. She is a good friend of the shop owner and regularly let her sons stay over there. Mr. Savoie, who described the dead brothers as "like an extended family", told Global News that he found a "horrific scene" when he checked on the boys at about 6am.

The Reptile Ocean pet shop 

"I thought they were sleeping and I've seen the hole in the ceiling, (and) everything has fallen. I turn the lights on and I've seen this horrific scene," Mr. Savoie said.

"I have so many mixed emotions right now. I can't believe this is real."

The python has been recaptured.

The local community expressed shock at what had happened. One neighbour said: "We could not believe that something like this could happen, but it has happened." But another Campbellton resident was less sympathetic. She said: "The fact that you have an apartment with animals like that below, the risk is always there."

Experts said attacks on humans by exotic snakes are extremely rare and, according to local officials, the reptile owner was fully licenced.

Exotic snake seller Alexandre Tremblay suggested the snake was "way under-fed and badly housed".

"For a snake to be able to get out of that size it just has to be really hungry and not in good conditions. Because usually snakes are very easy-going ... it's rare that snakes get out," he said.

Post-mortem examinations on the two boys' bodies are due to be carried out today.