The US Geological Survey says a magnitude-7.1 quake struck at 3.55am on Sunday (0255 AEST) at a depth of 40.6 kilometres. Its epicentre was 63 kilometres south-southwest of Vanuatu's capital, Port-Vila.
The temblor was followed by several aftershocks, including a magnitude-7.0 quake at a depth of 28.5 kilometres. Its epicentre was 69 kilometres south-southwest of Port-Vila. The Pacific Tsunami Warning Centre said no tsunami warning was issued.
Vanuatu, a chain of 83 islands, lies just over 2000 kilometres northeast of Sydney. It is part of the Pacific "Ring of Fire," an arc of earthquake and volcanic zones stretching from South America through Alaska and down through the South Pacific.