The earthquake that struck Christchurch has caused some 30 million tons of ice to break off from New Zealand's biggest glacier.

Tour guides at the Tasman Glacier in the Southern Alps say the quake caused the ice to "calve" from the glacier, forming icebergs in the terminal lake.

Tourists of Glacier Explorer boats say the icefall caused waves of up to 3.5 meters in height which swept up and down the lake for 30 minutes.

The glacier is about 120 miles (200 kilometers) from Christchurch on the west coast.

The powerful earthquake struck Christchurch on Tuesday, toppling tall buildings and churches, crushing buses and killing at least 65 people.