Police say they are following "strong lines of inquiry" after a man was shot and badly hurt on a Christchurch bridge last night.

The 29-year-old was shot once in the shoulder at around 8.20pm, near the intersection of Radley St and Ferry Rd, where a bridge crosses the Heathcote River.

It's understood the man was standing on the bridge when he was shot.

Armed police cordoned off the Woolston bridge last night until about 10pm, and took samples from bloody clothing.

Detective Sergeant Jo Carolan said the shooter was travelling in a vehicle and left immediately afterward.

The victim remained in hospital today, in a serious but stable condition.

Police were following strong lines of inquiry, Carolan said.

"Police believe those involved in this incident are known to each other and there is no risk to the general public," she said.

"We would like to hear from anyone who was in the Radley St/Ferry Rd area around the time of the shooting, who may have information which could assist our inquiries."