Heavy rain in the Whanganui River headwaters has Horizons Regional Council's emergency management staff on alert.
Officials were considering whether to erect a flood barrier at Whanganui's Kowhai Park.
The Whanganui River was expected to rise to 11m at Pipiriki just before 9am and continue to rise.
Emergency managers would then decide whether barriers were needed during the afternoon.
The peak height of the river alongside the city was expected to be 7.9m at the town bridge at 5pm.