The police dive squad has joined the search for a missing swimmer in Canterbury's Waimakariri River.

A police spokesperson said the squad is arriving on-site on Monday morning.

"Their search efforts will focus on the area between the two bridges, the State Highway 1 bridge and the Old Waimakariri bridge."

Police were called when the man's friends could not find him after he went swimming near the Waimakariri Bridge.

Despite police searching the river with help from the Kaiapoi Coastguard on Saturday night, the man could not be found.

The Kaiapoi Coastguard crew is hoping the swimmer will be found.

President Logan Pryce said they took a boat up the river late on Saturday night as far as the bridge, but were unable to find him.

"We always hope for a good outcome when these sorts of things happen but hopefully we can bring this guy home today would be nice."

He said river conditions were fine at the time.

The dive squad at the Waimakariri River on Monday. Photo / George Heard

Police said anyone with information about the incident should phone 105 and quote file number 210130/5446.