The quake was centered 23 kilometers (15 miles) from Port Olry and hit at a depth of 27 kilometers (17 miles), the agency said.
The Pacific Tsunami Warning Center said that a tsunami threat it had issued for nearby Vanuatu coasts has passed. There were no immediate reports of damage or casualties.
Vanuatu is home to about 280,000 people and is prone to natural disasters, with a half-dozen active volcanoes as well as regular cyclones and earthquakes. It sits on the Pacific “Ring of Fire,” the arc of seismic faults around the Pacific Ocean where earthquakes and volcanoes are common.