At least two people have died in New Zealand after a powerful magnitude-7.8 earthquake struck South Island.

PM John Key said further details were not yet known.

According to US Geological Survey, the tremor hit just after midnight, some 59 miles from Christchurch.

A tsunami arrived about two hours later. Officials warned everyone along the eastern coast to head inland or for higher ground.

According to Weatherwatch.co.nz, a gauge at Kaikoura,112 miles north of Christchurch, measured a wave of 8ft 2ins in the early hours of the morning.

At one point, the ministry of civil defense suggested tsunami waves as tall as 16ft could hit the eastern coast.

By just after 08:00 local time, the warning was scaled back to a “marine and beach threat” with waves of just 3ft along a small stretch of coast, including the Chatham Islands, an archipelago 423 miles south-east of the mainland.

Aerial images show tunnels along the coastal highway close to Kaikoura, a popular tourist destination, covered by a landslide. Other pictures of the devastated area show at least one collapsed home.

New Zealanders are used to earthquakes. The country lies on the notorious Ring of Fire, the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim.

Christchurch is still recovering from the 2011 earthquake that killed 185 people and destroyed the city center.