A New Zealand volcano that featured as Mount Doom in "The Lord of the Rings" movies is in danger of erupting as pressure builds in a subterranean vent, officials have said.

"The current situation can't continue, Ruapehu is so active that the temperatures have been going up and down a lot," DOC volcanic risk manager Harry Keys told Radio New Zealand.

"They generally haven't gone up as we've expected for some weeks now and sooner or later that situation will be rectified,