An underwater volcano off the coast of Tonga, a small Polynesian island nation in the South Pacific, has been erupting since December. Recently, the accumulating lava formed a new island.

As the volcano, named Hunga Tonga -- short for Hunga Tonga-Hunga Ha'apai -- erupted in recent weeks, dark smokey plumes could be seen bubbling out of the sea. Meanwhile, lava has slowly been hardening to form the new island, now measuring about a mile in length and a half-mile wide. It rises up some 820 feet from the ocean's surface.

The new islands were confirmed by satellite imagery, which show newly solidified rock formations and accumulating sediment in the sea.

"It's really quite solid once you are on it and it's quite high," Gianpiero Orbassano, a local Tonga hotel owner, told the BBC. He and a friend recently visited the newly formed island.

"It felt quite safe -- the only difficult thing was getting out of the boat on to the island. The surface was hot, you could feel it. And climbing it was hard in the bright sun."

The latest proliferation of lava is the second time Hunga Tonga has erupted in the last five years.