An aerial observation is being conducted over Mt Ruapehu today, after temperatures in the active volcano's bubbling crater lake rose to the hottest on record.

Yesterday, a tourist flight over the Crater Lake observed "vigorous steaming" at the lake and disturbance of the surface itself with "upwelling-bubbles".

This sort of activity had not been seen in years while Crown research institute, GNS Science, said a temperature of 44 degrees is "the hottest lake temperature we have recorded since the new lake was established post 2000."

A swarm of volcanic earthquakes reported on Tuesday had now stopped, however, seismic network at Ruapehu continues to record volcanic tremor.

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GNS volcanologist Brad Scott has been closely monitoring activity overnight and said there been only more tremor and an insignificant change in lake temperature of around 0.3 of a degree.

"There has been little to no change from yesterday -- activity has been dominated by volcanic tremors, with no distinct or individual volcanic earthquakes."

An observation flight organised by GNS this morning could provide a further indication what was happening on the mountain top, he said.

But the elevated tempertures did not neccessarily mean an eruption was imminent.

"In fact, if you track back through the record, sometimes it has erupted from cold lake temperatures. This is what makes it difficult for us, as there's no fixed pattern."

"In the end, it's an active volcano and we should always pay respect to it."

The developments weren't sufficient enough to upgrade Mt Ruapehu's Volcanic Alert Level, which remained at 1.

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.

Meanwhile, unrest was continuing at the volcano at White Island, where a minor eruption occurred last month.

While there hadn't been another event as large, small geysering at the crater and a series of volcanic earthquakes recorded there indicated there was still "significant unrest" at the offshore volcano in the Bay of Plenty, he said.