An explosion sent an 11-year-old boy to hospital with severe injuries this long weekend.

It happened at a late-night gathering on Canada Day in East Kildonan.

On Monday, Winnipeg police said the boy was playing with gun powder he found in a backyard and a metal pipe, similar to a plumbing pipe.

"A very tragic incident," said Const. Jay Murray. “We believe this child found a pipe at the address, and filled that pipe with gunpowder that was left out, and we believe that’s what he threw into a fire that caused an explosion," he said.

Police believe the boy had been alone for a short time, and others were nearby. Someone at the gathering called 911.

Officers said the boy was taken to hospital in stable condition, but has serious and life-altering injuries to his hand.

Investigators went to the home where the explosion happened, found a gun, and seized it.

They arrested a 41-year-old man, one of the boy's family members.

Police said people with an explosive device in their possession have a legal duty to prevent bodily harm, and in this case, gunpowder was not properly stored.

"For anyone that has gunpowder or that may make ammunition, here in the city or anywhere else, just maybe a reminder that it is an explosive material, and if that's accessible by anyone who isn't trained to work with it, it can cause injuries like this."

Officers didn't say how much gunpowder was used or how big the explosion was that led to the boy's hand injuries, but they did say it's expected he'll stay in hospital for a while.

Police haven’t released the specific nature of the relationship between the boy and the 41-year-old man.

The man was arrested for breach of duty related to explosives and unauthorized possession of a firearm.