The quake struck in the northern Pacific Ocean between the tip of the Aleutian Islands and Russia's Kamchatka Peninsula.

Civil Defence says a major quake under the ocean near Russia does not pose a tsunami threat to New Zealand.

The powerful earthquake hit off the coast of northeastern Russia, some 200 km from the city of Nikol'skoye on Bering island.

The quake was initially reported as a magnitude 7.7 before being revised down to 7.4 and finally upgraded to 7.8.

That magnitude represents a major earthquake, normally capable of causing widespread and heavy damage when striking on or near land.

It was also very shallow, only 10km below the seabed, which would have amplified its effect, but it was far from any mainland.

There is no tsunami threat to New Zealand following the 7.8M Komandorskiye Ostrova Russia earthquake. — MCDEM (@NZcivildefence) July 18, 2017

The quake struck in the northern Pacific Ocean between the tip of the Aleutian Islands and Russia's Kamchatka Peninsula.

The epicentre was west of Attu, the westernmost and largest island in the Near Islands group of the Aleutian Islands.

It sparked a tsunami warning from the Pacific Tsunami Warning Centre. Hazardous tsunamis were possible for coasts located within 300km of the earthquake epicentre, it warned.

Tsunami waves, however, were unlikely to reach Kamchatka's eastern coast, some 500km away.

Civil Defence said it was assessing the risk to New Zealand but swiftly confirmed there was no risk. There was also no tsunami warning for the South Pacific.

The quake was followed by several aftershocks, including a couple above magnitude 5.

- Stuff and Reuters