A devastating 6.3-magnitude earthquake struck the New Zealand city of Christchurch on Tuesday, killing at least 65 people and collapsing buildings onto victims, some of whom used their cell phones to frantically call for help, officials said.

The earthquake, the second to hit the city since September, struck at 12:51 p.m. local time as the city center teemed with pedestrians. Several people were reportedly in the tower of the Christchurch Cathedral as its spire toppled.

Local television showed bodies being pulled out of rubble; it was unclear whether any of them were alive. Footage showed bricks and shattered concrete from buildings strewn in the streets. Sidewalks and roads were cracked and split; dazed and crying residents, their faces bloodied, wandered the streets as sirens blared, some of them scurrying as parts of damaged buildings continued to fall.

Some cars were buried under rubble, and rescuers threw chunks of concrete aside to reached survivors.

Christchurch Mayor Bob Parker declared a state of emergency in the city of 400,000 residents. “”Make no mistake — this is going to be a very black day for this shaken city,”” he said.

For a time, large parts of the city were without electrical power or telephone services. Authorities ordered major hospitals nationwide to make room for victims.

The Christchurch Press newspaper reported that the initial quake was followed by constant aftershocks, some as powerful as magnitude-5.

Prime Minister John Key said at least 65 people had been killed. He rushed to the city after holding an emergency meeting with New Zealand lawmakers.

“”To be honest, it’s pretty grim,”” said Ian Stuart, a reporter for the New Zealand Press Association. “”The last earthquake in September didn’t kill anyone because people were home asleep when it struck. This one hit when the streets were filled with people. Some of them were calling emergency services and family members from their trapped places.””

The earthquake’s epicenter was reportedly 3 miles below ground about 12 miles southeast of Christchurch, a gateway city to New Zealand’s South Island. The Sept. 4 quake was a 7.1-magnitude temblor but the epicenter was deeper and struck much farther from Christchurch, officials said. There have been thousands of aftershocks in the area following the September quake.

Stuart said unconfirmed reports put the death toll at more than 90, with estimates that it could reach as many as 1,000.

“”The people of Christchurch were just believing they may be over the worst when the quake struck today,”” said Stuart.

A release posted on the website of the Christchurch police department said that “”the central city is currently being evacuated, as reports are received of widespread damage to buildings and infrastructure. Multiple fatalities have been reported at several locations in the central city, including two buses crushed by falling buildings. A doctor and emergency services are attending.””

The release listed several buildings that had collapsed, fires in other downtown structures as well as numerous victims trapped in the rubble.

“”There were screams from trapped people and others digging with their hands to free trapped people,”” Stuart said. “”I talked by phone with one woman who pulled her bed mattress on top of her. There are lots of old stone buildings in Christchurch and lots of those collapsed.””

Before rushing to the scene, Key told New Zealand legislators that many details were still unknown.

“”The worrying fear, of course, is that this earthquake has taken place at a time when people were going about their business — it is a very populated time, with people at work, children at school,”” he told parliament “”But we are aware of significant damage to buildings that had people in them at the time.””

Christchurch City Councilman Barry Corbett, who was on a top floor of a building when the quake struck, told reporters: “”When the shaking had stopped I looked out of the window, which gives a great view onto Christchurch, and there was just dust.

“”It was evident straight away that a lot of buildings had gone,”” he said.