Key Points:

A lahar warning system on Mt Ruapehu had been fully tested for the first time today, Conservation Minister Chris Carter said.

The multi-million dollar system, which included volcanic flood sensors and automatic gates, was tested with a multi-agency civil defence response, Mr Carter said.

"The results of the system test were very positive. People living in the Ruapehu district now have early warning of and protection from emergencies on one of the most active lahar paths in the world."

Lahars, or mudslides, from Ruapehu had been an ongoing hazard for more than a century, Mr Carter said in a statement.

The response system had been finally installed more than 50 years after the Tangiwai disaster.

In 1953, a lahar swept away the Tangiwai rail bridge, causing 151 deaths when a train plunged into the river.

Mr Carter said there had been 15 eruptions which had produced lahars since the 1953 disaster. One, in 1975, had created a lahar of similar size to the Tangiwai event.

Mr Carter said it was "absurd" that debate in recent years had revolved around digging a trench on top of Mt Ruapehu when excavation would do nothing to prevent future lahars.

A lahar is expected to take place before January 2005.

Councils from areas surrounding the mountain had asked the Government to try and prevent the lahar, which is expected to release hundreds of millions of litres of water trapped inside the volcano's lake.

However, the Government decided instead to install an early warning system to give people time to clear the area in the event of a lahar.

It has defended its decision by saying it was advised that taking measures to reduce a lahar would increase the long-term risk of one forming.

The Government's response plan includes an electronic alert system to provide 90 minutes' warning before the lahar reaches the Tangiwai Bridge; a 300m-long stopbank on the Whangaehu River to minimise the risk of the lahar spilling into the Taupo catchment; closing at-risk sites, bridges, roads and railway lines and raising the Tangiwai Road Bridge on State Highway 49.