5.7-magnitude earthquake and several aftershocks struck beneath the Pacific off New Zealand's Kermadec Islands  today, US geologists said, but no tsunami warning was issued.

The remote offshore quake hit at 05:42am (1742 GMT Saturday) at a depth of 32 kilometres (20 miles), 65 kilometres east of Raoul Island and 926 kilometres south of Tonga, the United States Geological Survey (USGS) said.

The USGS at first measured the quake at a strong magnitude of 6.2 but later downgraded it.

The Pacific Tsunami Warning Center did not issue an alert for the area, part of the Pacific's "Ring of Fire", a highly active tectonic zone that frequently experiences earthquakes.

The initial quake was followed by several aftershocks with a magnitude of more than five.

The remote Kermadec Islands are New Zealand's northern-most islands, more than 1,000 kilometres from Auckland.