NUKU'ALOFA, Tonga - A powerful 7.9-magnitude earthquake struck Friday in the Pacific Ocean, shaking an erupting underwater volcano off Tonga's main island and raising fears of increased lava and ash flows, officials said.
There were no immediate reports of injury or damage from the quake, which was felt more than 3,000 kilometres away in New Zealand. A tsunami warning for islands within 1,000 kilometres of the epicentre was cancelled two hours later.
"We are quite lucky not to get a tsunami," Tongan government chief seismologist Keleti Mafi told The Associated Press.
But he warned the powerful quake "will directly affect the eruption" of the volcano about 10 kilometres from the southwest coast of Tongatapu island and could lead to more molten lava and ash flowing into the sea. A column of smoke and steam was rising 20 kilometres into the sky.
"The strength of the earthquake could crack the volcano's (undersea) vent and allow more magma (molten rock) to be ejected," Mafi said.
A check of the volcano Thursday from a boat about three kilometres away from the vent showed about "a 10-metre depth of lava at the vent" standing up out of the ocean.
"It's grown out of the sea," he said, adding the violent eruption meant "it's very risky to go closer."
The quake struck about 200 kilometres south-southeast of the capital, Nuku'Alofa, at a depth of 10 kilometres, the U.S. Geological Survey said.
The agency recorded a 5.3-magnitude aftershock in the same region two hours after the initial quake.
Officials in the Tongan capital, Nuku'alofa, were relieved the 170-island archipelago appeared to have suffered no injuries or damage.
"Quite remarkable, given the magnitude of it. We might have gotten off lightly," the national police commander, Chris Kelly, said.
"The house really moved, the trees were swaying and the ground was rippling," he said.
Local resident Dana Stephenson said the quake started with "deep rumblings ... then side-to-side movement which seemed to go on forever but I guess was about 40 seconds - which is long enough."
Radio stations in Tonga broadcast warnings that people should move away from coastal villages due to the tsunami threat that Kelly said was later cancelled.
New Zealand seismologist Craig Miller said "a long, low rolling motion" from the quake was reported by residents on the east coast of New Zealand's North Island.
