CHRISTCHURCH, New Zealand (Bloomberg)—Christchurch residents are bracing for more aftershocks threatening to topple buildings already weakened by New Zealand’s deadliest earthquake in 80 years as the search for survivors enters a second full day.

“The rate of aftershock activity will decrease over the coming weeks but the magnitudes of the earthquakes don’t,” John Townend, associate professor of earth sciences at Wellington’s Victoria University, said in a telephone interview. “It’s going to be a question of many weeks and could be several months.”

The South Island city, New Zealand’s second largest, has been jolted by 37 aftershocks since Tuesday’s 6.3-magnitude temblor that killed at least 75 people, according to the Civil Defense Department website.

The city’s tallest building, the Grand Chancellor Hotel, is unstable and may be moving, police said. Workers stopped searching the collapsed remains of the Canterbury Television building because of safety concerns.

Police imposed a nighttime curfew in some areas of Christchurch amid concerns that more buildings may collapse. Members of the public within the center’s four main avenues after 6:30 p.m. local time will be arrested, police said.

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

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.

Trapped alive

About 300 people are unaccounted for with some possibly trapped in buildings and the Grand Chancellor has been evacuated, New Zealand Police said. More than 100 people may have died in the Canterbury TV building, the New Zealand Herald reported, citing police.

“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 enrolled at an education college in the city of about 400,000 are among the missing, Japan’s Ministry of Foreign Affairs said yesterday. One Australian is among the dead, Prime Minister Julia Gillard said.

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

City counts damage

The death toll from the 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.

Damage to central city buildings was greater than the September temblor because it was shallower and centered just 10 kilometers southeast of Christchurch, according to geonet.org.nz. The Sept. 4 quake was focused 55 kilometers northwest of the city and was also deeper.

Tuesday’s temblor struck at 12:51 p.m. local time during the lunchtime break, whereas the September temblor hit at 4:35 a.m. and claimed no lives.

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.

Yesterday, 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.

Flooding, cracks

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 began the task of checking buildings individually for survivors.

Some 80% of the city is without water, according to the New Zealand police website.

The quake may be the costliest natural disaster for insurers since 2008. Insured losses from the temblor may be $12 billion, Michael Huttner, an analyst at JPMorgan, said in a note to clients. That would be the most expensive calamity since the $19.9 billion loss from Hurricane Ike, which struck the U.S. in 2008, according to the Insurance Information Institute, a New York-based trade group.

Tuesday’s quake served as a reminder of the jolt in Christchurch on Sept. 4 that shook consumer confidence and contributed to a 0.2% drop in gross domestic product in the third quarter. The Reserve Bank of New Zealand estimates the September temblor caused $5 billion New Zealand ($3.7 billion) of damage.