(Reuters) - A major earthquake of 7.4 magnitude hit New Zealand, 30 km (20 miles) west of Christchurch early on Saturday morning, causing no immediate reports of casualties but widespread damage, authorities said.

The quake, which had a depth of 33 kms (20.5 miles), struck around 4.35 a.m. local time (1635 GMT Friday) and was felt throughout much of the South Island and southern parts of the North Island, but did not trigger a tsunami.

A STRONG earthquake has caused widespread damage and power cuts across New Zealand's second-largest city.

Shaken residents told how they cowered under doorways as the earth moved violently for what seemed as long as a minute.

The quake's magnitude was revised downwards slightly from an initial estimate of 7.4 to 7.2, the U.S. Geological Survey (USGS) said.

However, it was powerful enough to topple chimneys and walls and send frightened locals scurrying out of their beds to safety when the tremor hit at 4.30am local time.

USGS experts said the quake struck New Zealand's South Island 19 miles (30 km) from the island's largest city, Christchurch, at a depth of 10 miles (16.1 km).

A 7.0-magnitude earthquake has struck off New Zealand's South Island, the US Geological Survey has said.

The epicentre was 55km (35 miles) north-west of Christchurch, at a depth of 12 km (7.5 miles), it added.

Police reported widespread minor damage and local power cuts. Christchurch is New Zealand's second largest city with a population of about 386,000, but no casualties have yet been reported.

The Pacific Tsunami Warning Centre said there was a risk of a local tsunami.