There are still no reports of damage following earthquakes in Tonga and PNG yesterday.
The U.S. Geological Survey said a strong quake measuring 6.7 hit Tonga at half past four yesterday afternoon.
It was centred 145 km northeast of the capital, Nuku'alofa, at a depth of 50 km.
The same organisation said the New Britain region of Papua New Guinea was shaken by a 6.2 magnitude quake about ten minutes earlier.
A seismologist with Geoscience Australia said it was unusual to get two earthquakes of this magnitude occuring within half an hour of each other.
He said the Tonga quake was probably part of the aftershock sequence following a big quake on May the 3rd.
The seismologist said the latest quake had been centred too far away from the Tongan capital to cause major damage.
A journalist in the capital, Nuku'alofa, said the quake had gone largely unnoticed.
The earthquake in PNG is in a zone of volcanic activity and in an area known for tremors.