A magnitude-7.3 earthquake struck in the sea off Tonga late Friday, according to the US Geological Survey, sparking a tsunami warning that was later lifted.
The USGS said the quake hit 10 kilometres (six miles) deep, about 200 kilometres southeast of Neiafu, a town in the northeast of the Pacific archipelago nation, shortly before midnight local time (1100 GMT).
It initially gave the magnitude at 7.1, but later revised it up to 7.3.
This was followed about an hour later by a much smaller quake of 5.1-magnitude in a similar area.
"There is no longer a tsunami threat from this earthquake," said the Pacific Tsunami Warning Center at about 1:30 am.
It had earlier said "hazardous tsunami waves are possible for coasts located within 300 km of the earthquake epicenter".
The Tonga meteorological service had earlier used social media posts to urge people to "remain inland and high ground and please listen to radio until further advised".
It told sailors to head into deeper ocean for safety.
Seismic activity is fairly common around Tonga, a country of about 100,000 people spread across 171 islands.
In January this year, it was rocked by the eruption of the Hunga-Tonga-Hunga-Ha'apai volcano, one of the most powerful such events in modern times, according to researchers from the University of Bath.