Rescuers are racing to free around 120 people buried under the rubble of an apartment complex felled by an earthquake in southern Taiwan, as an investigation begins into the collapse that killed at least 34 people.

Key points: Rescuers continue to work to free victims of a deadly earthquake in Taiwan

Rescuers continue to work to free victims of a deadly earthquake in Taiwan Scores still trapped beneath rubble

Scores still trapped beneath rubble Questions raised over possible building violations

The death toll continued to rise on Sunday as emergency workers dug to find survivors of the 6.4-magnitude quake that toppled the 16-storey apartment complex containing almost 100 homes in the city of Tainan on Saturday.

Firefighters, police, soldiers and volunteers combed through the ruins, some using their hands, watched anxiously by dozens of the victims' family members who wore thick jackets, woollen hats and scarves to combat the winter chill.

Rescuers said 118 residents were still missing, with 103 of them trapped "very deep" in the rubble.

"There's no way to get to them direct, it's very difficult," Tainan Mayor William Lai said, adding that emergency workers were having to bolster the ruins to ensure they were secure before digging.

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One woman, Chen Yu-mei, told how her three-month-old son was trapped inside with her sister's family of seven.

"He's a small child, I'm worried sick," she said, her voice cracking and eyes red from crying.

Another woman, surnamed Chang, said she was waiting to hear from her 24-year-old daughter who lived on the fifth floor of the complex.

"She's not answering my phone calls ... I am trying to hold my emotions and stay strong. I'll do that until I find her," she said.

The building's lower floors pancaked on top of each other in the quake and then the whole structure toppled, raising immediate questions about the quality of materials and workmanship used in its construction in the 1990s.

Mr Lai said survivors and relatives had reported there were legal "violations" at the building, without giving any further detail.

"I've contacted judicial units and prosecutors have formally launched an investigation," Mr Lai said.

"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."

President Ma Ying-jeou is scheduled to visit the disaster zone on Monday, the first day of the Lunar New Year.

Meanwhile, survivors spoke of their terror and relief.

One man said he was rescued after tapping on a wardrobe that was trapping him.

"I knocked on the closet to get the attention of rescuers who broke the window to get me," said resident Su Yi-ming, 48, who lived with his family on the sixth floor of the Wei-kuan complex.

Mr Su escaped uninjured, with his wife and their two children sustaining minor injuries.

"We are very lucky that we are alive but I'm sad that some of my neighbours lost their lives," Mr Su said.

Crane plucks survivor from rubble

A survivor of an earthquake in Taiwan who was rescued by a crane is taken to an ambulance. ( AFP: Anthony Wallace )

Footage released by emergency workers showed rescuers talking to one trapped 36-year-old woman through the rubble, where she had been pinned down by furniture for 16 hours, before digging her out.

One survivor used a hammer to break out of her crushed home, while another tied clothes together to lower himself to safety, local media reported.

Another woman was extracted alive from the ruins by crane late on Saturday.

Wang Chih-peng, 38, was rescued with his wife and three-year-old daughter.

"I was scared awake by the quake and I held my wife and child until it stopped shaking," he said.

"We lay on our bed waiting for rescuers because we thought it safer.

"I heard the sound of rescuers approaching and screamed for help and they removed the window to pull us out. I saw the building had tumbled and luckily we were safe."

Taiwan lies near the junction of two tectonic plates and is regularly hit by earthquakes.

The island's worst quake in recent decades was a magnitude-7.6 tremor in September 1999, which killed about 2,400 people.

AFP/Reuters