The US Geological Survey (USGS) said that the quake occurred 109.4 km northwest of Neiafu, Vava'u, the largest town on the island of Tonga, and at a depth of 10 km.
There have been no reports of casualties or material damage as a result of the earthquake so far, and no tsunami warnings have been issued.
It could take several hours until authorities can conduct comprehensive damage assessments, especially in remote areas.
Aftershocks are possible over the coming days.
