The Tonga disaster office says there have been no reports of injury and little damage after the massive earthquake which hit the kingdom this morning.
Emergency services were put on full alert following the earthquake measuring 7-point-8 on the Richter scale.
The US monitoring centre says the epicentre was 155 kilometres south of Neiafu island and 160 kilometres north-east of Nuku'Alofa, the main island.
The deputy director of the disaster office, Male'u Takai, says they've made preliminary assessments in Tongatapu and the outer islands.
"No damages have been reported or injuries or fatalities - that includes buildings. There were no damages report on buildings or any other infastructure, except for the power supply in Tongatapu, it was disrupted. So we assume that everything is safe. But the police are doing a more detailed assessment of the situation and should be ready sometime later today."