No damage has been reported and a tsunami warning was not issued.
The tiny island nation of Tonga lies close to a major faultline and frequently experiences earthquakes and tremors.
It sits within the Pacific "Ring of Fire" - a geologically active area that encompasses parts of south-east Asia, Micronesia and the western side of the Americas.
Sizeable earthquakes have struck New Zealand, Indonesia, Papua New Guinea and Japan in recent weeks.
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