The quake occurred in the Tonga region, approximately 155 km from Neiafu island.
Niue, located to the east of the epicenter, has also been placed on alert.
According to the U.S. Geological Survey (USGS), the earthquake struck at 6:05 am AEST on Wednesday at a depth of 10 km.
The U.S. National Tsunami Center reported that no tsunami is expected following the quake.
Reuters