Coastguard Wanganui launched their rescue boat around 2.30pm and carried out a shoreline and river search. A helicopter was also used to search from the air and police patrols carried out searches of the banks on both sides of the river.
"We have grave concerns for his well-being and we are speaking with the man's family and friends," Mr Wright said.
"The search has been stood down for this evening but the police dive squad has been contacted and it is anticipated they will conduct a search of the river over the weekend."
Swimmers were visible above the little beach at Mosquito Point. It was high tide, and the current was visibly moving upriver.