Police and the Department of Corrections are investigating an incident at Christchurch Men's Prison in which a group of inmates used a home-made air gun to fire at the prison building.
The prisoners, who were working in the prison's engineering unit on Monday morning, attached a pipe to the end of an air compressor hose to fire ball bearings or other projectiles.
Assistant regional manager for Canterbury prisons Ian Bourke says no one was injured and he believes the inmates were retaliating to a random search under way at the time.
Mr Bourke says prisoners are assessed before they are allowed to use the workshop, but further steps may be needed to prevent a similar incident.
