NUKU'ALOFA, Tonga — A powerful 7.9-magnitude earthquake struck today 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 1,875 miles away in New Zealand. A tsunami warning for islands within 625 miles of the epicenter was canceled two hours later.

"We are quite lucky not to get a tsunami," Tongan government chief seismologist Keleti Mafi said.

But he warned the powerful quake "will directly affect the eruption" of the volcano about six miles from the southwest coast of Tongatapu island and could lead to more molten lava and ash flowing into the sea.

The quake struck about 130 miles south-southeast of the capital, Nuku'Alofa, at a depth of 6.2 miles, the U.S. Geological Survey said.

The agency recorded a 5.3-magnitude aftershock in the same region two hours after the initial quake.