The Pacific Tsunami Warning Centre says it's fortunate the wave generated by the earthquake near Tonga early this morning was not dangerous.
The quake struck at a depth of 10km and 210km from the Tongan capital, Nuku'alofa.
A geophysicist at the centre says the shallowness of the quake warranted the issuing of a tsunami warning for a thousand kilometre radius from the epicentre.
Dr Victor Sardina says earthquakes of the same magnitude have generated killer tsunamis in the past.
"The bottom of the ocean didn't deform in such a degree that would have generated a larger tsunami wave which is actually lucky, we were lucky this time again"
But Dr Victor Sardina says the earthquake may still have created dangerous currents in the sea and people should avoid the coast.