Scientists searching for exotic life forms living around seafloor methane seeps have also recovered chunks of frozen methane from along the edge of the continental shelf.
Little is known about the methane hydrate deposits around New Zealand, but they are attracting increasing attention as a potential fuel source for hydrogen cells that could generate electricity with the only emissions water and heat.
The National Institute of Water and Atmospheric Research discovered vents bubbling with methane off Wairarapa a decade ago, and Niwa's research vessel Tangaroa has just returned from a new survey of methane seeps along the continental slope of the North Island.
The Tangaroa brought up two chunks of methane ice - one of the first times scientists have held in their hands frozen methane from the deposits around the New Zealand coast.
"It was a fist-sized piece of dirtyish white material," expedition co-leader, Ashley Rowden said. "We could see immediately that it was hydrates: because of the release of pressure the methane was coming off it and it was fizzing and fizzing.
"It's unusual to be able to get a piece of it and bring it to the surface - but for energy requirements that will be the key," he said.
Methane hydrates are found in particularly high concentrations along the seafloor from Cook Strait to Gisborne - the "Hikurangi margin" - the route followed on the Tangaroa's latest voyage.
The team also collected samples of the sediment and water surrounding the seeps for chemical analysis and used sonar to study the geological structures lying beneath them.
The voyage, which ended this week, investigated the biology of the methane seeps and took a close look at the specialised organisms living there, but next year a joint German-New Zealand expedition will investigate geological issues - including the big methane hydrate deposits as a source of fuel.
The other co-leader of the Tangaroa trip, Amy Baco-Taylor, of the Woods Hole Oceanographic Institution in the United States, said the voyage was the first time cold seeps had been viewed and sampled in the southwest Pacific.
The 21 researchers from Niwa, Woods Hole, the Scripps Institution of Oceanography and the University of Hawaii spent two weeks exploring eight "cold seeps" where methane gas or hydrogen sulphide bubble out.
"This is the first time the biodiversity of the animal communities living at these sites has been observed directly and thoroughly documented, providing the first discovery of cold seep communities in the entire southwest Pacific," said Dr Baco-Taylor.
They have unique communities of animals living in symbiosis with microbes converting the energy-rich chemicals as nutrients, so that the organisms don't need sunlight as an energy source.
Similar organisms are seen on hot hydrothermal vents along the volcanic Kermedec Arc, and on large deposits of biological material, such as dead whales, and sunken logs.
The sites were at depths between 750m and 1050m, and one, labelled The Builder's Pencil, covers 180,000sq m - one of the largest seep sites in the world, according to Dr Rowden.
The scientists videoed and sampled 30-40cm long worms emerging from beneath limestone boulders.