The quake struck at a moderate depth of 100 kilometres (62 miles) with the epicentre some 85 kilometres north of the Tongan capital Nuku'alofa.

There were no immediate reports of damage.

The Pacific Tsunami Warning Center said there was no tsunami threat.

Baea Filimoehala from the reception at the Emerald Hotel in Nuku'alofa told AFP there was no damage in the capital, describing the quake as a "small one".