Churches across New Zealand have opened their doors to those in need following an earthquake in New Zealand.

The 7.8 magnitude earthquake hit the South Island, just after midnight on Monday morning.

A tsunami struck the island about two hours later.

Residents living along the coast were evacuated to nearby churches including the Rangiora Baptist Church.

Shortly after 8.00am, people who were evacuated in coastal Christchurch were given the all-clear to return home.

Near the epicentre, the quake opened up snaking fissures in roads and sparked landslides.

Officials said one person died in the town of Kaikoura on the eastern coast.

The town has also lost electricity and access routes by road are blocked.

A second person died in Mount Lyford, at a ski resort nearby.

Aftershocks continued throughout Monday morning.

Prime Minister John Key flew over the affected area by helicopter on Monday afternoon.

"It's just utter devastation. ... That's months of work," Mr Key said.

He estimated the clean-up would cost hundreds of millions of dollars and clearing the debris and blocked roads could take months.

The area is still recovering from a 2011 earthquake that killed 185 people.