If you are hearing reports of a lahar on Mt Ruapehu do not worry – it is just a drill.

GNS Science has carried out its annual practice run this afternoon across the mountain’s ski fields.

Spokesman Steve Sherburn says they have been timing the evacuation.

“It’s alright having a warning system, but you’ve really got to educate the ski field workers and the skiers on the ski field to make sure they respond to warnings when they really happen.”

Mr Sherburn says practice runs are essential because a lahar can travel from the crater lake to the top of the ski field in 30 seconds. He says the warning system gives people, in the worst case scenario, a minute to get away.