WELLINGTON: New Zealand Prime Minister John Key said two people were killed in a powerful earthquake that the struck the Pacific nation early on Monday.

"We don't have any indications at the moment to believe it will rise, but we can't rule that out," Key told reporters in Wellington, adding that details of the casualties were still being confirmed.

Key said a military helicopter was being dispatched to the coastal tourist town of Kaikoura, near the epicenter of the 7.8 magnitude quake, some 91 km (57 miles) north-northeast of Christchurch in the South Island.

New Zealand's Civil Defence warned residents along the country's entire east coast to seek higher ground.

Anna Kaiser, a seismologist at GNS Science said a tidal signal or surge of up to one meter (3 feet) had been recorded in North Canterbury region of the South Island.

"That's reasonably significant so people should take this seriously," she told Radio New Zealand.

The quake was centered 91 km (57 miles) north-northeast of Christchurch, the biggest city on New Zealand's South Island. A 6.3 quake there in February 2011 killed 185 people and caused widespread damage.

The tremor, which was measured by New Zealand's Geonet at magnitude 6.6, was felt throughout most of New Zealand. Civil Defence said it was too early to assess the damage or whether there had been any injuries or deaths.

"The whole house rolled like a serpent and some things smashed, the power went out," a woman who gave her name as Elizabeth told Radio New Zealand from her home in Takaka, near the top of the South Island.

Residents in Wellington said glass had fallen from buildings into the streets.

A series of aftershocks were recorded around the country, some as strong as 6.1 magnitude.