The National Crisis Management Center said the tsunami, moving across the Pacific at 800 kilometers an hour, could produce even higher wave heights by the time it reached New Zealand's main islands, where people in all coastal areas were warned to stay off beaches and keep out of rivers and estuaries.
Civil Defense Minister John Carter said "surges of huge volumes of water" were predicted around the coast and urged people to keep listening to radio reports and obey police orders.
Tsunami waves built up as they hit the Chatham Islands, rising from 20 to 50 centimeters and a third at 1.5-meters.
Officials said waves of 20 centimeters had been recorded on tsunami gauges at East Cape, Gisborne, Napier and Castlepoint on the east coast of the North Island, and bigger surges were likely to follow over a period of several hours.
Radio New Zealand reported unusual sea activity around the country with waters slowly receding large distances before rushing back to the beach.
Local councils closed beaches in some areas, and camping grounds in coastal areas were evacuated. Large ships left the ports of Napier and Lyttelton to ride out the predicted tsunami waves at sea.
The ferry service linking the North and South islands announced a changed timetable to keep its vessels out of port at predicted times of the tsunami's arrival, and a coastal railway line was closed.
Welfare centers were set up in several areas as police warned residents in towns and villages on the east coast of both main islands to move to higher ground or be prepared to evacuate.
People living in low areas of the Banks Peninsula, near Christchurch in the South Island, began leaving their homes for higher ground in the wake of predictions of waves up to 3 meters reaching the area later in the morning, Radio New Zealand reported.
Civil defense officials were put on standby in the capital, Wellington, and the country's biggest city, Auckland, as they awaited the predicted waves.
Scientist Ken Gledhill told Radio New Zealand it was very difficult to predict the size of waves, but every precaution should be taken.
He said the tsunami was not a one-off wave, "but more like a river coming toward you and going up and down."
