New Zealand said Thursday that only a "miracle" could save possibly hundreds of people trapped in the rubble after a devastating earthquake that has killed at least 76.
Two days after the 6.3-magnitude tremor laid waste to central Christchurch and some of its suburbs, police grimly reported there had been no communication with anyone caught in the wreckage for 24 hours.
"We are hopeful that we might find survivors, but as time passes hopes fade," superintendent Russell Gibson told TV3.
Prime Minister John Key said an estimate of 300 missing could prove to be "wildly inaccurate either way", and urged people to be realistic about finding more survivors in New Zealand's worst natural disaster in 80 years.
"That does not mean that there can't and won't be people trapped in buildings," said Key, adding that names and nationalities of some of the dead would be released later.
"All over the world when we see disasters like this, we see miracle stories of people being pulled out, days and in some cases weeks after the event," he told TV3. "We can't give up hope, but we also need to be realistic."
An English language school based in the six-storey Canterbury Television (CTV) building, which was razed to the ground, said 48 students and staff were missing, including 10 members of a Japanese study group.
Five of the students, who included citizens from a range of Asian countries, were on just their second day at King's Education college, which was on the building's third floor. Up to 100 people may be missing in the building.
Japanese search and rescue experts were on the scene and were combing the CTV site in the shadow of the listing, 26-storey Grand Chancellor Hotel, Christchurch's tallest building, which is at risk of collapse.
Australian, British, American, Taiwanese and Singaporean teams are also helping about 500 New Zealand rescuers comb several sites in the cordoned-off centre of the nation's second-biggest city.
Emergency workers will fan out to devastated suburbs on Thursday.
Up to 30 people were rescued on the first night but only a handful emerged from the wreckage on Wednesday, including one woman who spent 26 hours under her desk in the mangled Pyne Gould building.
Brief hopes were raised by a report of signs of life in the Holy Cross Chapel. But rescuers scrambling to the site were unable to find any survivors.
Rescue efforts are now entering their final stage, with New Zealand's emergency chief saying most trapped people will only be able to survive for two to three days.
Pyne Gould Corporation said rescue efforts at its four-storey block, which folded like a concertina, had now turned to recovering bodies rather than rescuing survivors.
It said 14 people were believed to be in the building.
Condolence messages have been sent from Queen Elizabeth -- New Zealand's head of state -- as well as US President Barack Obama, Pope Benedict XVI and the Dalai Lama.
New Zealand sits on the "Pacific Ring of Fire", a vast zone of seismic and volcanic activity stretching from Chile on one side to Japan and Indonesia on the other.
Christchurch was rocked by a 7.0-magnitude earthquake in September, which damaged 100,000 buildings but did not cause any deaths. New Zealand has not suffered such large loss of life since 256 people died in a 1931 quake.
Prime Minister Key on Tuesday announced New Zealand's first ever national state of emergency, allowing the country's resources to be directed towards the quake effort.