An undersea volcano is seen erupting off the coast of Tonga, sending plumes of steam, ash and smoke high into the air, on March 18, 2009 off the coast of Nuku'Alofa, Tonga. [CFP]

NUKU'ALOFA, Tonga -- An undersea volcano erupted off the coast of Tonga shooting clouds of smoke, steam and ash thousands of feet (meters) into the sky above the South Pacific ocean, officials said Wednesday.

Spectacular columns spewed out of the sea about 6 miles (10 kilometers) from the southwest coast off the main island of Tongatapu - an area where up to 36 undersea volcanoes are clustered, said Tonga's geological service head, Keleti Mafi.

"It's a very significant eruption, on quite a large scale," he told The Associated Press.

There was no sign the offshore eruption posed any danger to residents, he said, with trade winds blowing gas and steam away from the island.

Residents said the steam and ash column first appeared on Monday morning, after a series of sharp earthquakes were felt in the capital, Nuku'alofa.

"This is not unusual for this area and we expect this to happen here at any time," Mafi said, adding that a similar eruption took place there in 2002.

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