The Pacific Tsunami Warning Centre says an earthquake centred east of Tonga on Sunday evening may generate aftershocks, but not tsunami.
The 7.1 magnitude quake occurred in a remote area 195 kilometres off the coast, at a depth of 33 kilometres.
Although buildings in the capital Nuku'alofa shook for two minutes, no immediate damage or injuries have been reported.
Duty scientist Victor Sardina says although the shake was widely felt in Tonga, tsunami have been ruled out.
He says many earthquakes in the region rank at about 8 on the Richter scale, so this one was only of medium size.
Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions.
It is the location of the 10 strongest earthquakes in the world since 1900, all of which registered a magnitude of 8.5 or above.