The U.S. Geological Survey said a magnitude-7.1 quake struck at 3:55 a.m. at a depth of 25.2 miles. Its epicenter was 39 miles south-southwest of Vanuatu's capital, Port-Vila.
The temblor was followed by several aftershocks, including a magnitude-7.0 quake that struck at 5:19 a.m. at a depth of 17.7 miles. Its epicenter was 42 miles south-southwest of Port-Vila.
The Pacific Tsunami Warning Center said no tsunami warning was issued.
Vanuatu, a chain of 83 islands, lies just over 1,250 miles 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.
A magnitude-7.3 quake struck near Vanuatu on Dec. 26, causing a tsunami a few inches high but no damage.