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 (5:35 p.m. British time Friday) and was felt throughout much of the South Island and southern parts of the North Island, but did not trigger a tsunami.

Police in Christchurch, New Zealand's second-largest city with a population of about 350,000 people, closed the central business district of the city, with building facades falling into streets, crushing cars and blocking roads.

There's a lot of damage that I've been able to observe in the central city area, mainly of the old brick and masonry buildings, a number of those have got walls that have fallen into the street, Christchurch mayor Bob Parker told Radio New Zealand.

Police said there were widespread reports of houses being affected with broken windows, items thrown off shelves, toppled chimneys, with power and water services disrupted.

Officials were checking how severe the damage was in rural areas, closer to the epicentre, west of the city.

Ray O'Donnell, owner of a hotel in Darfield, a small farming community around 20 kms (12 miles) west of Christchurch, said large cracks had appeared in rural roads near the epicentre.

GNS Science, the New Zealand government seismological agency, gave the magnitude as 7.4. The U.S. Geological Survey initially reported it at 7.4 but later revised its figure to 7.0.

The city's airport was shut as a precaution as the runway and facilities were checked, and the railway network and bridges throughout the region were also being checked for damage.

The quake was felt as a long rolling motion lasting up to 40 seconds. The area was continuing to feel aftershocks as strong as magnitude 4.9.

No destructive widespread tsunami threat exists based on historical earthquake and tsunami data, the Pacific Tsunami Warning Centre said.

New Zealand scientists record around 14,000 earthquakes a year, of which around 20 top magnitude 5.0.

The last fatal earthquake in the geologically active country, caught between the Pacific and Indo-Australian tectonic plates, was in 1968 when an earthquake measuring 7.1 killed three people on the South Island's West Coast.

(Editing by Peter Graff)