Tuesday's heavy rain mainly affected farms on river flats near the mouths of the Whangaehu and Turakina rivers, Federated Farmers' Wanganui president Brian Doughty says.
Surface flooding of the low lying flats may have wrecked some crops.
Inland, the big dump made the land slip, destroying tracks, roads, culverts and fences. Swollen streams affected bridges, and surface flooding will make docking more difficult.
"We are sympathetic to those who have suffered loss and damage from one of the biggest rainfall events I can recall," Mr Doughty said.
His Brunswick farm received about 80mm of rain. The largest amount he's heard of was the 120mm that fell at Orautoha, near Raetihi.
The region was still discovering many knock-on effects. But Mr Doughty said the February 2004 storm was more widespread, and much worse.
Federated Farmers' main concern was for people who may be displaced or in need.
Ruapehu president Lyn Neeson was unable to get back to her Ohura farm until yesterday. Others went to their farms but have been unable to get out.
Some would need food, and others would need to urgently get to their farms to look after their animals.
Anyone who needs help should contact the Ruapehu-Wanganui Rural Support Trust on 0800 787 254 or Federated Farmers' Adverse Events line - 0800 376 844.
There was a silver lining to the rain event, Mr Doughty said.
"Given we're midway through spring, things were starting to get on the dry side. The volume of rain we received will have topped up ground water and boosted soil moisture."