The US Geological Survey said the quake was 535km (330 miles) southeast of Vanuatu island.
The Pacific Tsunami Warning Centre issued a local tsunami warning for areas close to the earthquake, though this was later cancelled.
There were no initial reports of damage or casualties.
Quakes are fairly common in the region. Two similar sized tremors last October and December caused no damage.
Friday's quake initially registered with a magnitude of 7.6 but was later downgraded. It was measured at a depth of about 10km.