A 16-year-old apprentice is "lucky to be alive" after falling seven metres at an Amaroo work site on Thursday morning, the building union has said.
WorkSafe ACT commissioner Greg Jones confirmed an investigation had been launched into how the teenage boy fell up to seven metres at the site of the new Coles supermarket on Horse Park Drive.
An ACT Emergency Agency Services spokeswoman said paramedics transported a 16-year-old with back pain to the Canberra Hospital after they were called out at 9.43am.
Mr Jones said the boy was in a stable condition in hospital and the site owners were fully cooperating with the investigation.
"The investigation is in its early stages but this could have been a serious incident," Mr Jones said.
"We'll be looking at whether the operator of the site needs to do anything to stop this from happening again and whether we need to take any action."
Dean Hall from the CFMEU said the boy was two days into his apprenticeship when the fall occurred.
"This child is extremely lucky to be alive after falling seven metres and landing on his head and shoulders. The question must now be asked [is] this child trained and supervised, a requirement by law. If this was your kid you would expect your child to come home to your unharmed," Mr Hall said.
Mr Hall said four construction workers have been killed in Australian in the last three weeks.
"Construction zones aren't war zones. Sixteen-year-olds can't go to war but they can go on construction sites. We as a community must demand better safety on construction sites," he said.