Mt Ruapehu in 'state of heightened unrest'

Mount Ruapehu and its Crater Lake are still in a state of unrest. Photo / Supplied

Scientists continue to monitor one of New Zealand's volcanic hot spots as underground rumblings reverberate.

Mount Ruapehu remained in a "state of heightened volcanic unrest", volcanologist Art Jolly said.

Last month, the mountain-top lake was measured at 46C - its highest temperature in over a decade - while an observation flight found it to be steaming.

It was now 32C.

There were moderate levels of volcanic tremors continuing.

Recent visits to the volcano have confirmed the output of volcanic gas - carbon dioxide, hydrogen sulphide and sulphur dioxide - remained elevated above background levels but was declining.

Water samples were collected from the Crater Lake for chemical analysis.

The lake temperature typically ranges between 15C and 40C, something which has been a common feature since it reformed between 1999 and 2000, having been removed by the 1995-1996 eruptions.

The last time it erupted was on September 25, 2007, causing a seven-minute-long earthquake, two lahars and flying rocks - one which crushed the leg of primary school teacher William Pike when it landed on Dome Shelter near the crater.

Since then, there have been warnings in 2008, 2011, 2012 and this year - all of which did not result in another major event.