Flood barriers have been deployed in Whanganui, and a watch is in place for the Manawatū River.
Slips have trapped about 120 tourists at Blue Duck Station near Taumarunui.
The barriers were activated as a precautionary measure.
Craig Grant from Horizons Regional Council said Whanganui River levels were expected to peak at over 10m early this evening.
He said the watch on Manawatū River would continue overnight.
A helicopter has delivered supplies and an emergency generator to the isolated lodges at Blue Duck.
The tourists would be stuck at the station overnight without power or water.
Horizons Regional Council said heavy rain had caused significant damage there.
At Pipiriki, 79km upriver from Whanganui, river levels have risen to more than 11m, 8m higher than normal.
Council spokesperson Ramon Strong said Whanganui River had been expected to peak at 7.9 metres about 5pm.
"We're monitoring it at the moment, and it's likely we'll install an inflatable barrier this morning if required. We're taking a precautionary approach but it's not going to be a major flood event."
Four roads in Pipiriki near Oyster Bluff, Horrocks Park and Kowhai Park were also closed by flooding.
In Wairarapa, Castlepoint was cut off due to slips on the Masterton-Castlepoint Road, and the Whangaehu Valley Road was blocked by fallen trees.
Members of the public are advised to take care while driving and check the AA's website for information on road conditions.