新西兰地震后发生强烈余震

A powerful aftershock shook New Zealand's South Island Monday, just hours after being hit by a powerful 7.8-magnitude earthquake.

John Kirby, a spokesman for U.S. Secretary of State John Kerry said the top American diplomat offered New Zealand "whatever U.S. assistance might be required."

New Zealand officials have confirmed two people died after the powerful earthquake hit 90 kilometers from Christchurch, the biggest city on New Zealand's South Island. The quake caused damage to buildings more than 200 kilometers away in the capital, Wellington.

Thousands of residents in the coastal area of New Zealand fled their homes for higher ground after tsunami warning sirens were activated in South Island coastal towns.

Some waves were up to two meters and officials described the tsunami as an "event of life-threatening or national significance."

A 6.3 quake in Christchurch in 2011 killed 185 people and caused widespread damage.