The first waves have started arriving in New Zealand after two strong earthquakes struck near Vanuatu.

The country is on alert after the Civil Defence force issued a tsunami watch earlier today.

A tsunami recorded off the coast of the Pacific Island measured just four centimetres, but officials here are urging caution on beaches.

"The first waves are now arriving and will be very small," said a Civil Defence spokesperson. "However it is expected that in most areas the largest waves will not arrive until many hours after the first arrivals.

"The 'potential threat' status remains in force. These waves will not be destructive but have the potential to create strong currents.

"Our advice remains for people on the West Coast from North Cape to Hokitika and on the East Coast from North Cape to Auckland to use extreme caution on beaches and stay out of the water as well as refrain from boating activities.