SYDNEY - A tsunami threat to Fiji has been cancelled, the Pacific Tsunami Warning Center said on Wednesday, shortly after a powerful earthquake struck off the South Pacific island nation, prompting many panicked coastal residents to evacuate to higher ground.

The quake, which hit at 10.52 am (2152 GMT Tuesday), was centred 280 km (175 miles) southwest of Fiji's capital, Suva, at a shallow depth of about 15 km (9 miles), the US Geological Survey said. It was originally recorded with a magnitude of 7.2 but was later downgraded to 6.9.

There were no initial reports of widespread casualties or damage.

Fiji's national disaster office issued a nationwide tsunami warning after the powerful underwater quake, leading to widespread evacuations and traffic jams.

"The earthquake caused a fair bit of panic, there are cars lined up trying to get to higher ground," said Jovesa Saladoka, the Fiji director of Oxfam.

Corrine Ambler, a Red Cross worker in Suva, said on Twitter all Red Cross staff and most of the capital was "headed to higher ground".

At least two aftershocks with magnitudes of more than 5 rattled Fiji soon after the quake.

The Pacific Tsunami Warning Center cancelled the tsunami threat to Fiji just over an hour after the first tremor.

There was no threat to nearby Pacific island nations Vanuatu and New Caledonia, authorities said.