CHRISTCHURCH, New Zealand — Police imposed a nightly curfew today in some sections of Christchurch, New Zealand’s second-largest city, amid concerns more buildings may collapse following the magnitude 6.3 earthquake that killed at least 75 people.

Members of the public who enter an area within the city center’s four main avenues after 6:30 p.m. local time will be arrested, according to the New Zealand Police website. Christchurch’s tallest building, the Grand Chancellor Hotel, appeared to be moving, police said. Workers have stopped searching the remains of the collapsed Canterbury Television building because of safety concerns.

Fifty-five victims have been named with another 20 recovered and awaiting identification, New Zealand Prime Minister John Key told reporters today. Rescuers are digging through wreckage left by Tuesday’s temblor, the nation’s deadliest in 80 years. Television images show one side of the 26-story Chancellor cracking and sagging.

“Today, all New Zealanders grieve for you, Christchurch,” Key said in Wellington as he prepared to board a plane for the wrecked city. “Many people have lost their lives. Families have lost their cherished loved ones. Mates have lost their mates.”

New Zealand declared a national state of emergency to coordinate help from outside the Christchurch region, according to the Civil Defense Department’s website. While people continue to present themselves at triage centers and hospitals, confirmed numbers of injured weren’t available.

Thirty aftershocks with a magnitude of 4 to 6 have been felt since yesterday’s temblor, the defense department said.

About 300 people are unaccounted for with some possibly trapped in buildings and the Grand Chancellor has been evacuated, New Zealand Police said.

“There are 30 people we’re aware that are trapped alive in a couple of buildings and there have been a number of bodies removed,” Aaron Gilmore, a National Party member of parliament, told Bloomberg Television.

Twenty-three Japanese students who were enrolled at an education college in the city of about 400,000 are included in the missing, Japan’s Ministry of Foreign Affairs said today. One Australian is among the dead, Prime Minister Julia Gillard said in Canberra Wednesday.

Australia sent 300 police and 140 Australian rescuers to join the relief efforts. Japan will send a 70-person emergency relief team, Prime Minister Naoto Kan told his nation’s parliament.

The death toll from the Tuesday quake, the strongest since September when the city was shaken by a 7.0 magnitude temblor, is the worst since the Napier earthquake in 1931 killed 256. The quake sent office workers fleeing into streets strewn with shattered glass, paper, bricks and broken concrete.

Damage to central city buildings was greater than the September temblor because it was shallower and centered about six miles southeast of Christchurch, according to geonet.org.nz. The Sept. 4 quake was focused 34 miles northwest of the city and was also deeper.

In the 17-story Forsyth Barr Ltd building in the city center, the stairwell collapsed and employees were lifted out by cranes, John Owen, a director at Forsyth Barr, said in a telephone interview. “It took four or five hours to get everybody out,” he said.

At midday today, an army helicopter circled a nearly silent city center almost 24 hours after the quake. At cordons, people talked to army and police staff as they tried to access homes or hotels. Others wheeled suitcases along deserted streets.

Cracks several meters long run along some streets. Other main roads swell with sandy mud and surface flooding stretching across footpaths and much of the roads.

On the corner of Gloucester Street and Oxford Terrace in the center, the 10-level Brannigans building’s windows have been shattered. Helmeted inspectors, meanwhile, checked buildings individually.

As reporters interviewed fire officers, an aftershock rippled the glass exterior of the Art Gallery, which is serving as the civil defense base. The shake toppled a chimney off the heritage-listed Art Center.

Rescuers are pulling survivors from several city buildings, as well as bodies, according to television reports. Searchers are in contact with some trapped survivors, Police Superintendent Russell Gibson said in a Television New Zealand interview. Some 80 percent of the city is without water, according to the New Zealand police website.

With lines stretching three blocks, residents Paul and Anna McElroy gave up waiting for water earlier today at the Phillipstown school in a suburb southeast of the city’s business center. They later returned to fill as many containers as possible once lines shortened.

“Water is what we need,” said Paul, 42, as he loaded soda bottles of water into the car. “They need more of these places. There are only six or so and it’s a real logjam.”