Updated December 31, 2019 15:44:41

A 40-year-old man in Brisbane has blown off his hand while mixing chemicals to make homemade rockets.

Photo: One of the homemade rockets set up for launch in the home's backyard. (ABC News: George Roberts)

Queensland police said the man's four-year-old son and a 74-year-old man were also in the Chermside West house when the explosion blew out windows and sent a shock wave through the home.

They said all three people were lucky to be alive as the force of the explosion could have been deadly.

The man was taken to the Royal Brisbane and Women's Hospital in a critical condition with a broken leg, a missing hand and other injuries.

He was rushed into the operating theatre for emergency surgery.

The toddler's mother was at work when the chemicals blew up about 8:00am.

Police say the man had been making rockets for a while, possibly to entertain his son.

"He's had a few successful launches in the past," Inspector Geoff Acreman said.

"We are very lucky we are not talking about three fatalities."

It is understood the 74-year-old and the toddler had been watching the man make the rockets but went upstairs before the explosion.

An elderly neighbour, who only wanted to be referred to as Bron, said the explosion had woken him.

"There was a bang, like a bomb, so I just got up from bed and looked though the window and smoke was pouring [out]," he said.

Photo: The backyard of the home with a homemade rocket set up. (ABC News: George Roberts)

Holly Barrett, whose balcony had a clear view across the road to the house where the explosion happened, said there were emergency service crews everywhere.

She said her housemate had seen the man come out of the house after the explosion.

"He was bloody all over the face, all over his arms, all around his chest," Ms Barrett said.

Police and paramedics have urged people not to mix or play with chemicals, even those commonly found around the house.

The investigation continues, with authorities trying to determine what the chemicals were being used for and why they exploded.

Photo: The explosion sent a shockwave through the home, which has been sealed off by police. (ABC News: George Roberts)

Topics: emergency-incidents, disasters-and-accidents, brisbane-4000, qld, australia, chermside-west-4032

First posted December 31, 2019 12:11:58