A navy ship sailing towards the Kermadec Islands has encountered a 25,000 square kilometre area of pumice pieces.
The area of floating pumice was estimated to be 250 nautical miles in length and 30 nautical miles wide.
The Royal New Zealand Air Force (RNZAF) Orion spotted the phenomenon yesterday afternoon, while on maritime patrol from Samoa to New Zealand.
The area of floating pumice is about 85 nautical miles off West South-West of Raoul Island.
Lieutenant Tim Oscar, a Royal Australian Navy officer described the phenomenon as "the weirdest thing I've seen in 18 years at sea".
He said the raft of pumice was moving up and down with the swell as far ahead as he could observe.
"The rock looked to be sitting two feet above the surface of the waves, and lit up a brilliant white colour in the spotlight. It looked exactly like the edge of an ice shelf," said Oscar.
RNZAF staff had been briefed by GNS Volcanologist Helen Bostock the previous day when the ship first encountered an area of pumice from an undersea volcano, believed to be New Zealand's third erupting volcano - the undersea Mount Monowai.
"I knew the pumice was lightweight and posed no danger to the ship. None-the-less it was quite daunting to be moving toward it at 14 knots.
"It took about 3 - 4 minutes to travel through the raft of pumice and as predicted there was no damage. As we moved through the raft of pumice we used the spotlights to try and find the edge - but it extended as far as we could see," said Oscar.
The Commanding Officer, Commander Sean Stewart changed course to intercept the pumice, and brought the ship to a halt to enable retrieval of samples.
The samples will be analysed to determine which volcano they