A magnitude 7.7 earthquake hit southeast of the Loyalty Islands in the French territory of New Caledonia on Friday.
According to the US Geological Survey (USGS), the quake was detected at a depth of 37 kilometres.
It hit southwest of Fiji, north of New Zealand and east of Australia.
"Based on the preliminary earthquake parameters, hazardous tsunami waves are possible for coasts within 1,000 kilometres of the earthquake epicentre," the Pacific Tsunami Warning Center said.
An eight-centimetre tsunami was observed in New Caledonia, according to Australia's Bureau of Meteorology (BOM).
A marine warning was issued for Australia's Lord Howe Island, BOM said.
A tsunami was forecast for Vanuatu, and smaller waves were forecast for Fiji, New Caledonia, Kiribati and New Zealand.
Following the earthquake, New Zealand's National Emergency Management Agency issued a warning for tsunami.
"We expect New Zealand coastal areas to experience strong and unusual currents and unpredictable surges at the shore," the agency said.