Two new aquatic species have been discovered at the halfway mark of New Zealand's largest ever scientific expedition to the Kermadec Islands.

A 13-strong team of scientists have been assessing fish, animal and plant species since departing on the Kermadecs Biodiscovery expedition on May 9.

They today announced they had found a pipe fish and a small left eye flounder which are likely to be new to science.

Auckland Museum marine curator Dr Tom Trnski said the pipe fish - which looks like a straightened out seahorse - was a particularly exciting discovery.

"We suspect the flounder doesn't grow very big as the largest one we have collected is just 10 centimetres long, but it's a pretty wee thing.

"Probably the most exciting find is the pipe fish - again it's small, just 10 centimetres long, and a white body with striking orange spots. Pipe fish are related to sea horses, and are really just like a sea horse that has been straightened out."

Other species, including a shark, a zebra lionfish, a tropical banded eel, a blackspot sergeant and a tropical goatfish, were also thought to be new to New Zealand records.

Dr Trnski said final confirmation of those species records won't be made until after the expedition returns in 10 days.

Department of Conservation botanist Dr Peter de Lange said previously undiscovered plants had also been found.

His team had uncovered three species of ferns thought to be new to records for the Kermadecs, he said.

DOC Entomologist Warren Chinn said he is also waiting for moths, bugs and flies he has collected to be identified.

Scientists expedition has been focusing their attention around Raoul Island, and the small islands nearby, at the northern end of the Kermadecs.

They will now move south to Macauley Island, where they'll carry out surveys around the four southern islands in the island chain over the next eight days.