UPDATED 4.47PM Corrections has highlighted the dangers to frontline prison staff after seven prisoners assaulted four officers in Christchurch last night.

They've been treated by their GPs after initial medical treatment on site, following the early evening attack.

Police say the assaults were physical and they believe an implement was used.

In a statement the Acting Prison Director Russell Watkins has reinforced that prisoners can be volatile and unpredictable, with many having long histories of antisocial behaviour.

He says their staff know assaults can happen and they receive specialist tactical training and personal protective equipment such as stab proof vests to keep safe.

Police have conducted a scene examination but they are yet to lay any charges.