WELLINGTON, New Zealand (AP) — A powerful earthquake struck New Zealand’s already-bruised city of Christchurch on Tuesday, collapsing buildings, burying vehicles under debris and sending rescuers scrambling to help trapped people amid reports of multiple deaths.

The 6.3-magnitude quake struck the country’s second-largest city on a busy weekday afternoon, in contrast to a major quake that damaged Christchurch last September but caused no deaths when it struck before dawn on a weekend. Police said there were reports of multiple fatalities from the latest temblor, while Prime Minister John Key told Parliament details of the deaths still were too shaky to confirm.

Witnesses said the quake destroyed the iconic stone Christchurch Cathedral, its spire toppled into a central city square, and police said there was a report of two buses crushed under falling buildings.

Live video footage showed sections of buildings collapsed into the streets, strewn with bricks and shattered concrete. Sidewalks and roads were cracked and split, and thousands of dazed, screaming and crying residents wandered through the streets as sirens blared.

Christchurch Mayor Bob Parker declared a state of emergency and ordered people to evacuate the city center.

“Make no mistake — this is going to be a very black day for this shaken city,” he said when asked about possible deaths.

The airport was closed and Christchurch Hospital was evacuated. Power and telephone lines were knocked out, and pipes burst, flooding the streets with water. Some cars apparently parked on the street were buried under rubble.

Some people were stuck in office towers and firefighters climbed ladders to pluck people trapped on roofs to safety.

“The details we have are extremely sketchy,” the prime minister told Parliament. “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. Sadly, I cannot rule out that there have been fatalities.

“But we are aware of significant damage to buildings that had people in them at the time,” he said.

Key said people were being told to get out of the city for their safety.

New Zealand police said in a statement that there were reports of multiple fatalities in the city, including a report that two buses had been crushed by falling buildings. The police statement said there were other reports of fires burning.

Gary Moore said he and 19 other colleagues were trapped in their twelfth floor office after the stairwell collapsed in the quake. He did not know if people on other floors were trapped.

“We watched the cathedral collapse out our window while we were holding onto the walls,” Moore said. “Every aftershock sends us rushing under the desks. It’s very unnerving but we can clearly see there are other priorities out the window. There has been a lot of damage and I guess people are attending to that before they come and get us.”

The multistory Pyne Gould Guinness Building, housing more than 200 workers, has collapsed and an unknown number of people are trapped inside. Television pictures showed rescuers, many of them office workers, dragging severely injured people from the rubble. Many had blood streaming down their faces. Screams could be heard from those still trapped.

Parker, the mayor, said he was on the top floor of the city council building when the quake hit just before 1 p.m. local time, throwing him across the room.

“I got down onto the street and there were scenes of great confusion, a lot of very upset people,” he said. “I know of people in our building who are injured and I’ve had some reports of serious injuries throughout the city.”

New Zealand’s TV3 said 24 people were trapped on the 17th floor of the 19-story Forsyth Barr office building, near the cathedral. The building was intact but a stairwell had collapsed, it said.

The network broadcast live pictures of rescuers accessing the building’s top story in gondola lifted by a crane and pulling people out one by one.

The U.S. Geological Survey said the temblor was centered 3 miles (5 kilometers) from the city at a depth of 2.5 miles (4 kilometers). A 5.6-magnitude aftershock hit shortly after 7 miles (11 kilometers) east of the city at a depth of 3.7 miles (6 kilometers).

“When the shaking had stopped I looked out of the window, which gives a great view onto Christchurch, and there was just dust,” said city councilman Barry Corbett, who was on one of the top floors of the city council building when the quake struck. “It was evident straight away that a lot of buildings had gone.”

Christchurch has been hit by hundreds of aftershocks since a 7.1 magnitude earthquake struck Sept. 4, which wrecked hundreds of buildings, and caused an estimated 4 billion New Zealand dollars ($3 billion) in damage, but caused no deaths.

A strong aftershock in December caused further damage to buildings.The city was still rebuilding from those quakes when Tuesday’s temblor hit.

Christchurch is home to about 350,000 people and is considered a tourist center and gateway to the South Island.

New Zealand sits on the Pacific “ring of fire” — an arc of earthquake and volcanic zones stretching from Chile in South America through Alaska and down through the South Pacific. It records more than 14,000 earthquakes a year — but only about 150 are felt by residents, and fewer than 10 a year do any damage.