An eruption detection system at one of the country's most active volcanoes has had a $1 million upgrade.
The system on Mt Ruapehu senses an eruption and within 30 seconds triggers a network of warning sirens.
The upgrade includes a new monitoring site at the top of the mountain, that runs on reticulated power, to replace the dome shelter near the crater lake which had been vulnerable to damage during an eruption.
The Department of Conservation says the new monitoring site is further away from the crater lake to make the system more reliable.
An eruption alert signal will also be sent across staff radios for the first time.
DoC scientist Dr Harry Keys says a volcanic mudflow or lahar could be at the top of the ski field 90 seconds after an eruption.
It was a lahar from the mountain that swept away the Tangiwai railway bridge in 1953 moments before a train crossed, resulting in the deaths of 151 people.
An even more powerful lahar swept down the mountain in March 2007, when the crater lake burst the banks built up after the mountain's eruption a decade earlier.
Dr Keys says the upgrade of the detection system is the result of lessons learnt from such events, and ongoing research.
It is a joint effort between DoC, GNS Science and snow fields operator Ruapehu Alpine Lifts.