A tsunami threat to Fiji has been cancelled, shortly after a powerful earthquake struck off the South Pacific island nation, prompting many panicked coastal residents to evacuate to higher ground, the Pacific Tsunami Warning Centre says.
The quake, which hit at 10.52am (8.52am AEST), was centred 280 km southwest of Fiji's capital, Suva, at a shallow depth of about 15 kilometres, 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," Jovesa Saladoka, the Fiji director of Oxfam, told Reuters by telephone from Suva.
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 Centre 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.
A magnitude-6.9 earthquake has struck 284 kilometres south-west of the Fiji capital Suva, the US Geological Survey (USGS) says.
The USGS said the quake was at a depth of 15.2 kilometres and an aftershock measuring magnitude-5.7 had also been recorded.
The Pacific Tsunami Warning Centre has withdrawn a tsunami warning for parts of the Pacific located 300 kilometres from the epicentre.
Radio New Zealand reported people had been evacuating the Fijian tourist hub of Nadi since the earthquake struck.
There have been no reports of damage or injury from Fiji.
"We felt it [the quake] ever so slightly in Suva," Sune Gudnitz, head of the United Nations' Office for the Coordination of Humanitarian Affairs said.
Red Cross Australia aid worker Susan Slattery said "pretty much everybody in Suva" evacuated buildings for higher land after the quake, fearing a tsunami.
"Certainly the whole city was on the move," she said.
"There are some level of earthquakes in and around Fiji fairly constantly or fairly often but this level of earthquake is unusual and certainly this close to the main islands is unusual and having the resultant tsunami warning is not common."
Kelvin Anthony said he was working in an office building in central Suva when a "slight tremor" was felt.
"Before the advisory came, one of our managers, who has sort of had, I guess, previously been in situations like this, quickly advised everyone that that's an earthquake and that we've got to move," he told the ABC.
"We also had power cuts, so it went on off, on off, about two or three times."
'Unusual' that tremor occurred away from plate boundary
Spiro Spiliopoulos, senior seismologist at Geoscience Australia, said the tremors happened close to a tectonic plate boundary between the Australian plate and the Pacific plate, where a large number of earthquakes are recorded.
"This is unusual in that it occurred a little bit away from the plate boundary," he told the ABC.
"They have the potential to generate tsunamis."
Geoscience Australia said main tremor would have been felt in the Pacific islands of Vanuatu, New Caledonia, Tonga and parts of American Samoa.
A magnitude-6.3 quake hit 582 kilometres south of Suva on Monday at a depth of 555 kilometres.
A swarm of more than 250 small earthquakes has struck since New Year’s Eve near the California-Mexico border, causing unease among residents and attention from scientists.
The earthquakes struck in the southern end of the Brawley Seismic Zone, a region that connects the San Andreas and Imperial faults, which can produce major earthquakes.
The earthquakes struck in the southern end of the Brawley Seismic Zone, a seismically active region where tectonic plates are moving away from each other and the Earth’s crust is getting stretched out “and basically adding land,” said Caltech seismologist Egill Hauksson.
The Brawley Seismic Zone is particularly important to watch because it is the region that connects the San Andreas and Imperial faults, both of which can produce damaging earthquakes. The seismic zone extends for about 30 miles from the city of Brawley, across the Salton Sea’s southern half, and ends near Bombay Beach.
Earthquake swarms that occur in the other end of the Brawley Seismic Zone — to the north — could trigger a major event on the San Andreas fault, one of California’s most dangerous, that could send catastrophic shaking into Riverside, San Bernardino and Los Angeles counties.
In late September, one such swarm began in the northern Brawley Seismic Zone, with three measuring above magnitude 4. That event led the U.S. Geological Survey to warn that chances of a magnitude 7 or greater earthquake on the San Andreas fault had risen as a result of the swarm.
Another swarm of small earthquakes, topping out at magnitude 3.5, struck the town of Niland near the eastern shore of the Salton Sea on Halloween.
Brawley Mayor Sam Couchman said the earthquakes have placed the city of 26,000 on edge since Saturday afternoon.
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