Gibson said the operation had become one of body recovery, though he rejected suggestions that rescuers were abandoning hope of finding anyone alive.
"Yes, we are still looking for survivors," he said on National Radio. "There are pockets within a number of these buildings and, provided people haven't been crushed, there is no reason to suggest we will not continue to get survivors out of there."
He said the search continued in the Canterbury Television building, but "the signs don't look good. There has been a fire in there ... We will continue to pull that building apart, piece by piece, until we are satisfied" there are no more survivors.
So far, 76 bodies had been brought to a temporary morgue, and the number was expected to rise as searchers pored through the thousands of buildings damaged in the quake, Police Superintendent Dave Cliff told a news conference Thursday.
He said 238 people were still listed as missing, but officials have cautioned that not all of the missing should be assumed dead.
Many sections of the city lay in ruins, and police announced a nighttime curfew in a cordoned-off area of downtown to keep people away from dangerous buildings and to prevent crime.
Six people had been arrested since the quake for burglary and theft, Cliff said late Wednesday, announcing that anyone on the streets after 6:30 p.m. without a valid reason could be arrested.
One of the city's tallest buildings, the 27-floor Hotel Grand Chancellor, was showing signs of buckling and was in imminent danger of collapse, Fire Service commander Mike Hall said. Authorities emptied the building and evacuated a two-block radius.
Parker said 120 people were rescued overnight Tuesday, while more bodies were also recovered. About 300 people were still unaccounted for, but this did not mean they were all still trapped, he said.
Key, the prime minister, said early Wednesday that the death toll stood at 75 and was expected to rise. The figure had not been updated by nightfall.
The true toll in life and treasure was still unknown, but the earthquake already was shaping as one of the country's worst disasters.
JP Morgan analyst Michael Huttner conservatively estimated the insurance losses at $12 billion. That would be the most from a natural disaster since Hurricane Ike hit Texas and Louisiana in 2008, costing insurers $19 billion, according to the Insurance Information Institute.
Key said the New Zealand economy could withstand the impact of the quake, the second to strike Christchurch since September.
"Christchurch's economic activity will be much less for a while," he told TV One. "The government will be doing everything it can to economically get Christchurch back on its feet."
Rescuers who rushed into buildings immediately after the quake found horrific scenes.
A construction manager described using sledgehammers and chain saws to cut into the Pyne Gould Guinness building from the roof, hacking downward through layers of sandwiched offices and finding bodies crushed and pulverized under concrete slabs.
One trapped man died after talking awhile with rescuers, Fred Haering said.
Another had a leg pinned under concrete, and a doctor administered medicine to deaden the pain. A firefighter asked Haering for a hacksaw. Haering handed it over and averted his eyes as the man's leg was sawed off, saving him from certain death.
"It's a necessity," Haering said Wednesday. "How are you gonna get out?"
The quake struck just before 1 p.m. local time on Tuesday, when the city was bustling with commerce and tourism. It was less powerful than the 7.1 temblor that struck before dawn on Sept. 4 that damaged buildings but killed no one. Experts said Tuesday's quake was deadlier because it was closer to the city and because more people were about.
Christchurch's airport reopened Wednesday, and military planes were brought in to fly tourists to other cities.
Officials told people to avoid showering or even flushing toilets, saying the damaged sewer system was at risk of failing. School classes in the city were suspended, and residents advised to stay home.
Christchurch's main hospital was inundated with people suffering head and chest injuries, said spokeswoman Amy Milne. But officials said the health system was coping, with some patients moved to other cities.
Tanker trucks were stationed at 14 spots throughout the city where residents could come to fill buckets and bottles, civil defense officials said, and people asked to catch and save rainwater.