CHRISTCHURCH, New Zealand (AP) — A powerful earthquake struck one of New Zealand's biggest cities today at the height of a busy workday, toppling tall buildings and churches, crushing buses and killing at least 65 people in one of the country's worst natural disasters.

It was the second major quake to hit Christchurch, a city of 350,000, in five months, though today's 6.3-magnitude temblor caused far more destruction than a stronger September quake that struck before dawn on a weekend. More than 100 people, including as many as a dozen visiting Japanese students, were thought to be trapped in the rubble as darkness — and drizzling rain — fell yesterday night.

In this image made from video run by New Zealand's TVNZ, men carry wounded man after pulling him out from rubble in Christchurch, New Zealand, after a strong, 6.3-magnitude earthquake rocked the city today. (AP Photo/TVNZ via Associated Press Television News)

In this image made from video run by New Zealand's TVNZ, men carry wounded man after pulling him out from rubble in Christchurch, New Zealand, after a strong, 6.3-magnitude earthquake rocked the city today. (AP Photo/TVNZ via Associated Press Television News) 1/1

"It is just a scene of utter devastation," Prime Minister John Key said after rushing to the city within hours of the quake. He said the death toll was 65, and may rise. "We may well be witnessing New Zealand's darkest day."

The spire of the city's well-known stone cathedral toppled into a central square, while multi-story buildings collapsed in on themselves and streets were strewn with bricks and shattered concrete.

Sidewalks and roads were cracked and split, while thousands of dazed, screaming and crying residents wandered through the streets as sirens and car alarms blared. Ambulance services were quickly overwhelmed, and groups of people helped victims clutching bleedings wounds, and others were carried to private vehicles in makeshift stretchers fashioned from rugs or bits of debris.

Nathanael Boehm, a web designer, said he was standing near a tram track when the quake struck just before 1:00 pm, sending the eaves of buildings cascading onto the street below.

"It was horrific. People were covered in rubble, covered in several tons of concrete," Boehm said, adding that he believed some of them had been crushed to death.

Christchurch Mayor Bob Parker declared a state of emergency and ordered people to evacuate the city centre. He said it was impossible to say how many people were trapped in the rubble, but that it was estimated to be more than 100.