A search and rescue operation is underway after a man failed to return from the Waimakariri River in Canterbury on Saturday night.
Police were called about 6.45pm after the man's friends were unable to locate him after he had gone for a swim near the Waimakariri Bridge, police said in a statement.
A search of the river, with assistance from the Kaiapoi coastguard, did not locate the man Saturday night.
The police national dive squad has been deployed and is expected to assist in the search on Monday.
Anyone with information about the incident is asked to call 105 and quote file number 210130/5446.