Undersea volcanic eruption visible from space

A volcano is erupting under the ocean in the Bismarck Sea, prompting warnings of possible tsunamis from authorities as ash and smoke bellow into the sky.

Papua New Guinea authorities have warned of falling pumice, ash, unpredictable swells and turbulent currents in the area near the eruption of the provisionally-named Titan Ridge Volcano.

Satellites have captured the event unfold from space, while seafarers in the area have seen it unfold.

One fisherman, Kennedy Masis, was searching for tuna when he "saw smoke coming out of the sea", he told the ABC.

"Twelve years as a fisherman I've never seen anything like that … it's scary.

He said the next day he saw plenty of dead fish near the reef which was like a "boiling spring".

He warned other fishermen in the region to be cautious in the area as the eruption continued.

Steve Saunders, the principal geodetic surveyor at the Rabaul Volcano Observatory, told ABC's Pacific Beat localised tsunami activity was possible.

"We could have some more intense explosive activity, in which case we may get just small tsunamis," Mr Saunders said.

"That would cause just small tsunamis because it's 100 kilometres at least to the nearest land."

He added that the ocean in the area is about 500 to 800 metres deep.

He said that while undersea eruptions had happened before, this one was showing some unique characteristics.

"We are getting pumice actually reaching the surface ... so it looks as though we may have a vent at, or very near the surface."

PNG's Mineral Resources Authority (MRA) said that the volcano was active along a 5km stretch of ocean, but regular satellite monitoring had been hampered by cloud cover in recent days.

A magnitude-5.4 earthquake was recorded near the site on Monday.

Before the eruption authorities recorded a number of quakes in the area, including six on May 8.

Mr Saunders said that any toxic fumes from the eruption were not blowing toward populated areas.