The earthquake struck in the Pacific Ocean between Tonga and Fiji, the US Geological Survey said.

A powerful magnitude 8.2 earthquake struck in the Pacific Ocean close to the islands of Tonga and Fiji on Sunday, the US Geological Survey (USGC) said.

But the undersea quake was too deep to trigger a tsunami, according to the US Pacific Tsunami Warning Center, which said small tsunami waves have been observed but no damage reported. There were no reports of casualties.

"I would not expect any damage. People will feel it but it's so deep that I would not expect any damage," USGS geophysicist Jana Pursley told Reuters.

A Civil Defence spokesman said there was no tsunami threat to New Zealand following the quake.

READ MORE: Explainer: After an earthquake, how does a tsunami happen?

The quake hit at a depth of 347.7 miles (559.57 kilometres) and was initially reported as magnitude 8.0 before being revised up to 8.2 by the USGC. No casualties are expected based on initial readings.

The epicentre was 167 miles (270 kilometres) east of Levuka on Fiji's Ovalau Island and 275 miles (443 kilometres) west of Neiafu in Tonga, a town with a population of around 6,000 people.

Fiji Seismology Unit director Apete Soro said the earthquake occurred closer to the Lau group of the islands, 62 km from Waiqori village.

There were also reports of the quake being felt in the central and western parts of the main island Viti Levu, he said.

They were still trying to reach out to places in the Lau group for any damage reports.

Samantha Rina from Fiji's capital in Suva said they felt the earthquake at 12.30pm.

I thought my head was spinning," she said.

"When the spinning didn't stop I got up, that's when I realised it was not in my head."

She said her neighbours were all drawn outside and everyone was talking about "ripples" they felt.

"It just felt like the earth rippled, like how one feels when in a boat out at sea, except this was on land and the house felt like it was rocking.

"It lasted a few seconds but we all felt it here. Then I saw the news of the quake."

The area of the quake lies in the notorious Pacific Ring of Fire, a region around the Pacific Ocean where several tectonic plates meet, causing earthquakes.