A massive earthquake with a magnitude of 7.8 rocked the island nation of Tonga on Thursday, triggering a panic evacuation in a New Zealand town after tsunami warnings were briefly issued for the South Pacific.

Although the warnings were withdrawn within two hours, hundreds of people in the New Zealand coastal town of Gisborne, more than 2,200 kilometres (1,375 miles) from the quake's epicentre, fled their homes.

"Most of the coastal communities in Gisborne evacuated," regional civil defence controller Richard Steele told national radio.

"Things got a bit out of control."

But while there was panic in New Zealand, the 110,000 residents of Tonga were unaware a tsunami warning had been issued.

"Due to a breakdown in an internal communications' system, the

Tonga authorities received no warning at all. Also, there seemed to be no internal mechanism for warning," said Kevin Vang of the Australian-Pacific Centre for Emergency and Disaster Information.

The US Geological Survey (USGS) said a "great" quake, initially measured at magnitude 8.0, struck at 4:26 am (1526 GMT Wednesday) in the middle of the islands that make up Tonga.

The epicentre was recorded 160km northeast of Tonga's main island of Nuku'Alofa and 16km below the Earth's surface, a relatively shallow distance which increases the likelihood of a tsunami.

It was the largest earthquake recorded by the USGS since a 8.6 temblor off the Indonesian island of Sumatra in March 2005, and immediately sparked fears of a repeat of the 9.0 Asian tsunami which killed 220,000 people in December 2004.