An earthquake measuring 6.3-magnitude hit New Zealand at 12:51 pm (2351 GMT) on Monday at a depth of 4 km, about 175 km northeast of Noumea, New Caledonia, said the U.S. Geological Survey.

Police suspect more fatalities than expected in Christchurch area, says Reuters. The quake was the second in five months, toppling buildings, causing injuries, trapping people beneath rubble and sparking fires, said the report.

The tremor was centred about 10 km (six miles) southwest of Christchurch, which had suffered widespread damage during last September's 7.1 magnitude quake but no deaths.

Christchurch is built on silt, sand and gravel, with a water table under it. In an earthquake, the water rises, mixing with sand.

Unlike last year's even stronger tremor, which struck early in the morning when streets were virtually empty, the streets, shops and offices in the city of almost 400,000 were thronged with people when the shallow tremor struck.

It's huge, it's just huge, a priest told a TV reporter outside the remains of the city's stone cathedral, part of which had been reduced to a pile of large sandstone blocks.

I just don't know whether there are people under this rubble, he said, before he appeared to add in a quiet voice: I think so.

Prime Minister John Key, who called an emergency cabinet meeting for later in the day, told parliament: This is a very populated time with people at work and children at school. Sadly, I cannot rule out whether there have been fatalities or not. But we are aware of significant damage to buildings that had people in them at the time.

News of the quake helped send the New Zealand dollar to as low as $0.7541 , down about 1.2 percent from late U.S. levels on fears the damage could dent confidence in the already fragile economy.

There has been a lot of damage, our TVs have been smashed and there are big cracks in the house. Neighbours have lost brick fences, Nicholas Hextall, who lives in central Christchurch, said by phone. Power and water had been cut.

The region has been struck by thousands of aftershocks since the original quake.

New Zealand, which sits between the Pacific and Indo-Australian tectonic plates, records on average more than 14,000 earthquakes a year, of which about 20 would normally top magnitude 5.0.