Corrective Services Minister Joe Francis says he does not have concerns about security at the privately-run Acacia Prison, despite prison staff discovering a "significant hole" in a fence at the medium-security jail.
The Department of Corrective Services has confirmed that an investigation into an attempted breakout is under way after prison authorities foiled an escape allegedly planned by a number of inmates.
The department said there was no breach to the prison's perimeter security and there was no risk to the community.
Those responsible for the alleged escape have since been moved from the Wooroloo prison, which houses about 900 male prisoners and is managed by detention services provider Serco.
Mr Francis said the prisoners were "never anywhere near" escaping and the public was not at risk throughout the incident.
"There's 5000 people behind bars in WA - many of them are dangerous criminals and many of them spend an awful lot of time while they are behind bars trying to think of creative ways to get out," Mr Francis said.
"What has happened at Acacia this week is exactly what should have happened. The system has worked. They were detected very early in their plan.
"I'm not going to go into the operational issues of it, but you can rest assured there was never any threat to the public of these people getting out."
WA Prison Officers Union secretary John Welch said Mr Francis' comments that the system had worked the way it should have were "simply wrong".
He blamed poor staffing levels for the incident, saying the union had raised its concerns over a shortfall in staffing with Serco a week-and-a-half before the incident.
"Clearly once the fence breach was identified staff did a very good job of managing it," he said. "But the question is how did we get to the point where a major hole was being cut in the fence? There were six people intending to go through it.
"You don't cut through that type of fence with a pair of kitchen scissors. It would have taken a considerable amount of time and effort."
Mr Francis said the union had taken a "cheap shot" at Serco and said he had full confidence in the operation of the prison.
Shadow corrective services minister Paul Papalia said the incident raised "very deep concerns" about the competency and capability of a privatised prison.