A tsunami began travelling across the Pacific on Thursday towards New Zealand and Tonga after a powerful 7.7-magnitude undersea earthquake, the Pacific Tsunami Warning Center said.
Tsunami waves were measured off Raoul Island, one of New Zealand's Kermadec Islands, up to a height of 0.84 metres (2.7 feet) above normal sea level, the centre said.
"Sea level readings confirm that a tsunami was generated," the centre said. "This tsunami may have been destructive along coastlines of the region near the earthquake epicentre."
The tsunami could reach Tonga by 2017 GMT and the eastern cape of New Zealand by 2052 GMT, the centre added, advising that if there were no damaging waves for two hours after the initial warning, local authorities could assume the threat had passed.
The quake struck at 07.03am Thursday (1903 GMT Wednesday) at a depth of just one kilometre (0.6 miles), the United States Geological Survey (USGS) said.
Its epicentre was 160 kilometres (99 miles) east of Raoul Island and 914 kilometres from the Tongan capital, Nuku'alofa.
USGS revised the quake's magnitude slightly downward from an earlier reading of 7.8.