People will gather at the site of the Tangiwai disaster tonight to remember those who lost their lives in the accident 64 years ago.
Tangiwai disaster - this was New Zealand's worst ever rail accident, killing 151 people on 24 December 1953 Photo: New Zealand Railways Corporation collection
The crash on Christmas Eve 1953 killed 151 people and is the worst railway disaster in New Zealand history.
The crater lake on Mt Ruapehu collapsed and created a lahar as about two million cubic metres of water surged downstream, collecting rocks, silt, trees, ice and other debris along the way.
It then shattered the Tangiwai Bridge across the Whangaehu River, just before the train arrived.
Minutes after the river hit, the Wellington to Auckland express thundered towards the damaged bridge.
Six carriages went into the river killing 151 people - 134 others survived thanks to a man swinging his torch by the bridge to alert the train driver, Charles Parker.
A memorial to Mr Parker and locomotive fireman Lance Redman was unveiled earlier this year.
Tonight at 10.21pm - the exact time the train went into the water - a candlelight vigil will take place at the site.
Tangiwai Memorial Committee chair Bob Norling said about 60 people were expected at the service.
"We will sing carols, say prayers and speeches and lay a reef in memorial to those who lost their lives."
Mr Norling said an upgrade of the site was planned with new information boards, bridge lookouts and planting.
"It's a big project and will take about five years - we are working towards the big 75th anniversary.
"More and more tourists and young people are visiting the site but it's pretty bare at the moment so we need to put more information there, we want people to spend time there and soak it all in and remember what happened that night," Mr Norling said.
The current rail bridge at Tangiwai with a deceptively calm Whangaehu stream running under it. Photo: RNZ / Eric Frykberg
-RNZ