PORT VILA: Two powerful earthquakes triggered a tsunami alert over a huge swathe of the South Pacific Thursday, sending residents fleeing to higher ground, just days after giant waves killed 177 in the region.

Vanuatu, Fiji, Tuvalu and New Caledonia sounded sirens and evacuated coastal areas after a 7.8 quake struck off Vanuatu at 9:03 am (2203 GMT), followed by a 7.1 tremor 10 minutes later, the US Geological Survey (USGS) said.

"We are trying to get those people staying closer to the coast to move inland," said Tuvalu's acting police commissioner Titelu Kauani.

The Pacific Tsunami Warning Center issued a tsunami warning for some 25 regional nations and territories including as far afield as Australia, New Zealand and Indonesia, before cancelling it about two and a half hours later.

But the warning center cautioned that the tsunami may have wrought damage close to the quake zone and that it was up to local authorities in each country to give the all-clear to residents.

"Sea level readings indicate a tsunami was generated," the center said, without giving any indication of the size of the wave or whether it was capable of causing damage.

"It may have been destructive along coasts near the earthquake epicenter," it said. "Danger to boats and coastal structures can continue for several hours due to rapid currents."

The alert came just eight days after an 8.0 earthquake hurled giant waves at Samoa, American Samoa and Tonga, obliterating entire villages and killing 177 residents and foreign tourists.

The new threat saw Fiji evacuate many coastal areas, closing schools and offices, while disaster management officials urged hotels to take tourists to higher ground.

In the capital Suva, police and soldiers stopped people from entering the central city area.

New Caledonia sounded warning sirens and ordered people away from the coast on the main island and eastern Loyalty Islands.

"Some schools have already been evacuated in the Loyalty Islands and sirens are going to sound soon for the population to find shelter and get away from the coast," a New Caledonia civil security spokesman told AFP.

Similar action was taken in Tuvalu, whose population of around 12,000 is settled on low-lying coral atolls.

Samoa, American Samoa and Tonga were among the countries put on tsunami alert even as they were beginning the slow process of recovering from last week's devastating waves. Related article: Panic in Samoa

Indonesia was also rocked by a catastrophic 7.0 earthquake last week which is feared to have left some 3,000 people dead on Sumatra island.

Only minutes before Thursday's Pacific quakes, the Philippines was hit by a strong 6.7 tremor.

The countries sit on the so-called Pacific "Ring of Fire", where the meeting of tectonic plates causes frequent seismic activity.

"This is a very active area -- and it's been very active over the last week-and-a-half," Dale Grant of the USGS told Sky News.