WELLINGTON, New Zealand >> A powerful 7.4-magnitude earthquake struck much of New Zealand’s South Island early Saturday. No tsunami alert was issued and there were no reports of injuries or serious damage.

The temblor hit at 4:35 a.m. (6:35 a.m. Friday, Hawaii time), shaking thousands of residents awake, New Zealand’s National Radio reported.

The Pacific Tsunami Warning Center in Ewa Beach said “no destructive widespread tsunami threat existed, based on historical earthquake and tsunami data.”

The quake, which hit 19 miles west of the southern city of Christchurch, shook a wide area with some residents there saying buildings had collapsed and power was severed.

Christchurch police reported some road damage in parts of the city of 400,000 people, with a series of sharp aftershocks rocking the area. Police officers cordoned off some streets where rubble was strewn about from the quake.

Christchurch resident Colleen Simpson said panicked residents ran into the street in their pajamas. Some buildings had collapsed, there was no power, and the mobile telephone network had failed.

“Oh my God. There is a row of shops completely demolished right in front of me,” Simpson 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,’ it was like the house got hit. It just started shaking. I’ve never felt anything like it,” he told the news website.

The earthquake was 21 miles below the Earth’s surface, the geological agency GNS Science said. Radio reports said items were tossed from store shelves and roof tiles cracked by the strong temblor.

New Zealand sits 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 felt by residents. Fewer than 10 a year do any damage.