The quake struck at a depth of just 9.4 kilometres (six miles) about 315 kilometres northwest of the Luganville, part of the Vanuatu archipelago, at 8:16am but no tsunami warning was immediately issued.

The region has been pummelled by some 20 aftershocks after yesterday's triple tremors measuring 7.6, 7.8 and 7.3 sparked a tsunami warning for much of the South Pacific, sending thousands of residents fleeing from the coast.

The Pacific is still recovering from last week's 8.0 magnitude earthquake and huge tsunami which crashed into Samoa, American Samoa and Tonga, wiping out villages and resorts and killing 184.

Samoa was holding a national day of mourning including a ceremony at Apia stadium and a mass funeral for 11 of the victims.