Two earthquakes measuring 6.2 on the Richter scale have been recorded in Vanuatu and Sumatra.
The United States Geological Survey said an undersea quake measuring 5.7 on the Richter scale struck 67 kilometres west of the capital Port Vila at a depth of 51km at 10am (local time) on Monday.
Another earthquake measuring 6.2 struck Indonesia's island of Sumatra 10 minutes later.
Two powerful earthquakes struck Vanuatu last month, one of which measured 6.5.
The quake in Vanuatu shook buildings and scared tourists but caused no significant damage.
In Port Vila, police said there had been no reports of injury or serious damage.
The Pacific Tsunami Warning Centre based in Hawaii did not issue a tsunami alert.
Vanuatu and Indonesia sit on the "Pacific Ring of Fire", a meeting point of continental plates that causes high volcanic and seismic activity.