A group of inmates attempted to escape their cell block at Alice Springs prison through a roof.
Fifteen prisoners tore through a ceiling and entered a crawl space, United Workers Union Northern Territory secretary Erina Early said.
Their bid for freedom ended when a corrections officer noticed some of the men were missing during a check of their cells and raised the alarm.
But it was a flawed attempt from the start.
"Every time a prisoner tries to leave their cell or their block it is considered as an attempt to escape, but they couldn't go anywhere as it was just a crawl space," Ms Early told AAP on Wednesday.
"It wasn't like Die Hard (the Bruce Willis movie)."
She speculated intense heat in the overcrowded prison that doesn't have air conditioning may have contributed to the men's bid to escape.
The maximum temperature in the desert city climbed above 35C on 22 days in December and 20 days in November, according to the Bureau of Meteorology.
The men, aged between 18 and 20, were housed in maximum security G-block, which was extensively damaged during riots in 2022.
Ms Early said repairs to the cell block had not been completed despite promises from NT Correctional Services and the justice minister.
The poor state of the facility enabled the inmates to climb into the roof and was a risk to officer safety, she said.
"You could have had a situation where these prisoners were waiting for officers and could have jumped on officers."
Ms Early said it was a concerning situation and corrections officers had a right to a safe workplace.
"The repairs should be a priority," she said.
The NT Department of Attorney-General and Justice said an investigation was under way, and there was no evidence the attempted escape was a result of conditions at the Alice Springs Correctional Centre.
"Staff and prisoners were not harmed during the incident, and the dormitory ceiling has been repaired," a spokesman said in a statement.
NT Correctional Services is also investing in security system upgrades and renovations at the prison for the safety and well-being of staff and inmates, the statement said.
United Workers Union represents prison officers.
