Earthquake strikes New Zealand's South Island

Quake measuring 7.4 on the Richter scale hits west of Christchurch, with residents reporting collapsed buildings

A powerful earthquake measuring 7.4 on the Richter scale struck New Zealand's South Island tonight.

The quake hit 19 miles west of Christchurch, on the south of the island, at 4.35am local time. It shook a wide area with some residents reporting collapsed buildings, bridges and power cuts.

Christchurch, which has a population of around 400,000 people, was also rocked with a series of sharp aftershocks. Minor injuries have been reported but no deaths.

Colleen Simpson, from Christchurch, said panicked residents ran into the street in their pyjamas. She said some buildings had collapsed, there was no power, and the mobile telephone network had failed. "There is a row of shops completely demolished right in front of me," she told the Stuff news website.

Another person from Christchurch, Kevin O'Hanlon, said the jolt was extremely powerful.

"I was awake to go to work and then just heard this massive noise and 'boom'," he said. "It was like the house got hit. It just started shaking. I've never felt anything like it."

Bruce Russell, 50, said that although he lives in Lyttelton, a port town to the south of Christchurch, which is on firmer volcanic ground, the earthquake had been "very alarming."

"We were woken up at 4.30am and it swayed like a ship at sea," he said. "It was very alarming. We have no power, which is a problem across [Christchurch]. We're listening to reports on a wind-up radio. It's still very frightening."

Russell said he had not experienced an earthquake on this scale before.

There were local reports of looting on one of Christchurch's commercial shopping streets and police were advising residents to stay inside until given an all-clear.

The geological agency GNS Science said the earthquake struck at a depth of 21 miles below the Earth's surface and the Pacific Tsunami Warning Centre said "no destructive widespread tsunami threat existed, based on historical earthqake and tsunami data".

New Zealand lies above an area of the Earth's crust where two tectonic plates collide. The country records more than 14,000 earthquakes a year – but only about 150 are usually felt. School children in the country often undertake earthquake drills.