Scientists will today have another attempt to check Mt Ruapehu's crater lake after sensors which indicate an impending lahar triggered on Wednesday night.

Department of Conservation scientist Harry Keys says a volcanic earthquake broke a cable which is part of the lahar warning system. Strong winds and cold temperatures have prevented staff from flying over the mountain to check whether there had been a lahar or an eruption.

Dr Keys say there was no sign of a mud flow in the Whangaehu River, however a high risk warning is in place.

Ruapehu Mayor Sue Morris says the mountain appears to have had a small "burp" which is under control at the moment. She says no one knows when mud will break over the walls of the crater lake causing a lahar to flow down the mountain, but the possibility is always on the minds of locals. Ms Morris says the council has good emergency procedures in place, should a lahar be triggered.

DOC is advising people not to proceed past the summit peaks and the crater rims between them. The Whangaehu, Mangaturuturu and Whakapapaiti Valleys are designated a medium risk.