The Whangaehu River at Kauangaroa is expected to peak at a level of 6.5m at 8am on Sunday.
Strong winds are also likely to be a problem over the weekend, Mr Smith said. MetService has forecast winds of up to 140km/h for Whanganui for Saturday morning.
"Residents are advised to secure loose objects and take care as the waterlogged ground may make trees unstable. Drive to the conditions if you are travelling."
Mr Smith said the Whanganui Emergency Operations Centre has been set up to monitor the situation.
"If river level actions remain as predicted there will be no full activation of the emergency operations centre. Emergency management staff will be at work through the weekend and will be monitoring river levels closely overnight Saturday through Sunday, and other staff are on standby if required."
During the weekend, up-to-date weather information for Whanganui can be found at www.metservice.com/towns-cities/whanganui.