A very large earthquake in Papua New Guinea had Civil Defence scrambling overnight, to decide if there was a tsunami threat.

The quake itself was just before midnight, with a magnitude of 7.9.

National Civil Defence Controller Sarah Stuart-Black said the protocol in situations like this it is to play it safe.

"We have an agreement with GNS science that based on the size of that earthquake and in that location that we would issue a national warning for a tsunami threat."

She said a nationwide coastal warning was issued, while the experts assessed the risk.

"And because it's Papua New Guinea, it's at least four hours away before any potential wave could affect New Zealand, so there's time for that assessment to be carried out."

Once it clear there was no risk, the warning was cancelled - at 1.20 this morning.

The official tsunami cancellation message related to the mag 8 eq in PNG has now been issued. We hope the rest of your night is peaceful.

— MCDEM (@NZcivildefence) December 17, 2016