The death toll rose as emergency workers dug for survivors of the 6.4-magnitude quake that toppled the 16-storey complex of almost 100 homes in the city of Tainan yesterday.
Officials said an investigation had been launched as questions were raised over the safety of the residential blocks in the complex.
Tainan mayor William Lai said survivors and relatives had reported "violations" but gave no further detail.
"We've also commissioned three independent bodies to preserve evidence during the rescue so we can assist the residents if they want to file lawsuits in the future. We will hold the builder responsible if they have broken the law."
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Local media reported the construction company that built the complex had gone out of business and also raised questions over the quality of the materials used.
Yueh Chin-sen, whose mother-in-law's family of eight is still trapped, said the residents had complained of defects in the building.
"They complained that the building wasn't well constructed as there were cracks in the walls and tiles fell off after several quakes in recent years," he told AFP.
Officials said 121 people are still unaccounted for, according to CNA news agency. Earlier, Lai said 103 residents were still trapped "very deep" in the rubble.
"There's no way to get to them direct, it's very difficult," Lai said, adding that rescuers had to shore up the ruins to ensure they were secure before digging.
Emergency workers used cranes, ladders and sniffer dogs to trace and extract survivors in their desperate search.
Several survivors were pulled from the rubble today, more than 24 hours after the quake struck, as rescuers urged those still trapped to stay strong.
Around 300 have been rescued so far, CNA reported.
Among those confirmed killed by the quake, at least 27 died in the apartment complex collapse, including several children.