A second, weaker, earthquake has rocked the South Pacific this afternoon, four hours after an 8.2 magnitude quake struck the region.

The second 6.2 magnitude quake was registered at 4.29pm local time at a depth of 465km with an epicentre located slightly north of the first.

The first earthquake struck at 12.19pm in the Pacific Ocean near the island nations of Tonga and Fiji at a depth of 566km.

The quake is reported to have generated small tsunami waves but a Civil Defence and Emergency Management spokesman said there was no threat to New Zealand.

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The US Pacific Tsunami Warning Centre said small tsunami waves had been observed.

"No hazard is expected for any coastline, but please be observant and exercise normal caution."

New Zealanders caught up in the first quake have described the moment the strong tremor hit.

Cara Michael, who is in Fiji with her family, said "buildings were swaying, made you feel a bit seasick almost, but it stopped after about half a minute".

Despite that, everyone was "pretty relaxed here as you'd expect", she told the Herald.

Another Kiwi, James Wilson, was holidaying on Tonga's main island of Tongataou when he felt the quake.

"I was on Queen Sālote wharf in Nuku'alofa, sitting on a bench and the bench started rocking."

"Had been cycling all morning, so thought it was just my legs feeling the workout from the bike, but now know it was the quake," Wilson said.

Graham told the Herald he was on a small Tongan island off Nuku'alofa when the ground began to shake.

"Sitting on the beach. It was a great shake which had us all looking at each other in disbelief, then thinking of high ground. Only thing higher than sea level was the coconut trees. Then heard no threat through the internet. All good here in Tonga."

Another New Zealander, from Christchurch, described the quake as a "gentle roll" which lasted for what seemed like a few minutes.

"Given we are from Christchurch, it wasn't nice," she said.

One person in Lautoka, the second biggest city in Fiji, said they felt the whole building shake, making them think it was flexible.

No casualties are expected based on initial readings and there have been no reports of damages.

The quake was not on the fault line where the Pacific Plate and the Indo-Australian Plate meet.

The plates runs almost the entire length of New Zealand's South Island.

The quake hit at a depth of 559.57km and was initially reported as magnitude 8.0.

The epicentre is 270km east of Levuka on Fiji's Ovalau Island and 443km west of Neiafu in Tonga, a town with a population of about 6000.