Two unsung heroes of the Tangiwai railway disaster will today have a monument unveiled in their honour.

On Christmas Eve in 1953, the rim of Mt Ruapehu's crater lake gave way and unleashed a lahar into the Whangaehu River, taking out part of the Tangiwai bridge.

All but three carriages of the Wellington to Auckland train plunged into the river moments later, killing 151 people.

General manager of operations at KiwiRail, Rob McAlpine, said it would've been worse if it wasn't for two people.

Engineer Charles Parker, who initiated an emergency break, and locomotive fireman Lance Redman, who sanded the train tracks to help the train break faster.

He said the two men have not been singled out before.

A service will be held alongside the unveiling of the monument.

Chairman of the Tangiwai Memorial Committee Bob Norling said the men deserve to be honoured.

"If it [hadn't] been for these two men and what they did - the heroes of the night - for sure the whole train would've gone into the Whangaehu River," he said.

Mr Norling said the pair's actions stopped the last three carriages from going into the river.

"134 people survived that night, out of 286 that were on the train - so their contribution was fantastic."