Beijing: Four trapped survivors, including an eight-year-old girl and a woman found shielded under the dead body of her husband, have been rescued alive from a collapsed apartment building, more than two days after a powerful earthquake struck southern Taiwan.

But local officials warned the prospect of finding further survivors was diminishing with every passing hour and that the final death toll from Saturday's 6.4-magnitude quake in Tainan may well exceed 100.

The official death toll had climbed to 40 by Tuesday morning; all but two from the collapsed 17-storey Wei Guan apartment where dozens of residents remain buried under folded piles of concrete and rubble, in a tragedy that has cast a shadow on Taiwan's Chinese New Year celebrations.

The rescue of eight-year-old Lin Su-Chin, more than 60 hours after the quake, provided a rare morale boost to rescue crews.

"She is awake, but looks dehydrated," Tainan mayor Lai Ching-Te told reporters. "I asked her if there's anything wrong with her body. She shook her head."

Television crews captured the dramatic rescue of another man, 42-year-old Lee Tsung-tian, whose girlfriend died in the collapse. That came hours after Tsao Wei-ling was found under the body of her husband, who died shielding her from a collapsed beam. But as well as her husband, her two-year-old son was found dead, and another five of her family members remain unaccounted for; a snapshot on the devastation wreaked on many families.

Distraught relatives have kept vigil at the site of the apartment collapse, with many others waiting at an information centre for news of their loved ones. But patience has increasingly worn thin as families deal with an agonising wait.

"Does that mean we are here to wait for bodies?" grandfather Liu Meng-hsun cried out angrily, when he was told there was still no news about their daughter-in-law and two young grandsons.

As questions continue to grow over whether a lack of structural integrity contributed to the building's collapse, Taiwanese president-elect Tsai Ing-wen said during a visit to the affected area in Tainan said her administration would make safety checks of old buildings a top priority, to ensure they can withstand earthquakes which occur frequently in Taiwan.

Images of the collapsed building, which was built in 1983, have clearly shown rectangular cooking oil cans lining the pillars of the collapsed apartment, fuelling speculation online as to whether they pointed to shoddy construction practices.

But local media reports, including the semi-official Central News Agency, said the cans were unlikely to have been load-bearing, and were more likely used for aesthetic purposes just under a wall's outer plaster. The use of the recycled cans was common before building codes were updated in 1999, with Styrofoam and formwork boards used now instead for interior structures like fake pillars and feature walls.

The Taiwanese government has promised an investigation into the building's collapse to determine if corners had been cut during its construction.

With agencies