Frontline police officers in Canterbury will remain armed after gunfire was exchanged on Tuesday night with a man who sustained critical injuries.

The decision was made by Canterbury District Commander Superintendent John Price that all frontline officers would carry firearms until further notice.

A shotgun-wielding man failed to stop for police on Breezes Rd about 7.20pm on Tuesday.

Road spikes were used on his car before he fired at police, with four bullets striking a police car. Police returned fire using Bushmaster rifles and Glocks.

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The man was shot in the lower body and was taken to hospital where he was under armed guard.

The gunman had tried to evade police after allegedly firing on officers just days earlier.

It's understood that he had been hiding out after reportedly firing at a police car during an early morning pursuit on Saturday.

The decision to bolster frontline staff with firearms is a decision that is made at district-level and will be reviewed at the commencement of each shift, according to police.

"The decision to arm all officers is not one that is taken lightly, but I believe it was necessary in this instance, to ensure the safety of police staff and members of the public," Price said.

"Police ensure that staff are equipped and enabled based on the environment and application of our risk assessment framework.

"Police are still seeking one other person in relation to the incident in Wainoni on Saturday morning."