Australia's Lord Howe Island is on alert after a 7.6 magnitude earthquake near New Caledonia.
The quake hit at 12.20am Australian eastern time on Thursday.
It was followed by at least three tremors in the region with magnitudes ranging from 6.0 to 6.2 in just over an hour.
An earthquake with a magnitude between 7 and 7.9 is considered a major event and can cause serious damage.
The more than 300 residents of Lord Howe Island, 600km east of the NSW mid-north coast, have been told to be on alert for dangerous rips, waves and strong currents.
People must stay away from beaches or any foreshore areas.
"At this stage, no evacuations are required at Lord Howe and no impact is expected for the Australian mainland," the Australian Bureau of Meteorology said.
Tsunami waves of around 40cm have been observed in the Pacific Ocean.
The bureau added waves of around 35 centimetres had already been observed at the Gold Coast in Queensland.
Geoscience Australia said the quake's epicentre was about 400km east of Tadine, New Caledonia, and was at a depth of 54km.
"Sea level observations have confirmed a tsunami has been generated," the Joint Australian Tsunami Warning Centre said in a bulletin.
"People in areas with the threat of land inundation and flooding are strongly advised by emergency authorities to go to higher ground or at least one kilometre inland."
A similar tsunami warning was issued for New Zealand, and residents along its northern coast have also been told to avoid beaches and shore areas.
