A girl aged eight and three others were rescued Monday from the rubble of a Taiwan apartment tower complex, more than two days after it was felled by an earthquake, but over 100 others remain trapped in the ruins.

Questions about the disaster intensified after images from the site showed metal cans and foam had been used to fill parts of the complex's concrete framework.

The girl and a 28-year-old woman were the latest to be pulled from the rubble, while a man and a woman were rescued earlier in the day as emergency workers scrabbled to find the missing.

Prosecutors have launched an investigation into the collapse of the 16-storey Wei-kuan building -- the only high-rise in the southern city of Tainan to crumble completely when the 6.4 magnitude struck before dawn Saturday.

The quake left 37 confirmed dead, most of them from the apartment complex. There were also some dramatic escapes.

Rescuers told earlier Monday how they took more than 20 hours to free one survivor, 40-year-old Lee Tsong-tian who was trapped by his leg.

He was eventually freed but had to have his leg amputated.

The other survivor pulled from the rubble earlier Monday was Tsao Wei-ling, 45, who is in stable condition.

Her husband and two-year-old child were pulled dead from the rubble, officials at the site said. A search was continuing for five other members of her family trapped inside.

- Safety questions -

City mayor William Lai said survivors and relatives had reported building violations.

The island's President-elect Tsai Ing-wen, who will take office in May, said her government would prioritise building safety.

"There are many old buildings across Taiwan... there should be an overall review of their resistance to earthquakes and other disasters," she said during a hospital visit to survivors.

Local media reported the company that built the complex had gone out of business.

Max Lo, former president of the Taiwan Engineering and Science Association, told AFP cans and foam could acceptably be used within decorative parts of a building to reduce its weight.

"Using them in the main structure would be against the national building code," he said.

"The first floor of the building was a shopping mall. We also need to find out if the walls designed to help support the building were taken out to increase the shopping space."

President Ma Ying-jeou said there was still hope for survivors, even beyond the 72-hour window which ends early Tuesday.

"We will carry on until the last second. The golden 72 hours of rescue is the standard but there are many exceptions," said Ma after visiting two survivors in hospital with bone fractures.

One of them, Liu Yi-chen, had lost her 10-day-old baby and husband. Her two other children remain missing.

The other had lost her husband, while her son and pregnant daughter-in-law are missing.

"Many people are still trapped and our hearts are sinking," said Ma.

Liu, a nurse, told AFP she was lying in bed breastfeeding her baby in their ninth-floor apartment when she felt the bed shaking. Then the floor caved in and she and her husband plunged several storeys.

Liu's legs were pinned down by bricks. Her baby fell nearby but she could not reach her.

"I was talking to my husband and told him we have to get out together. He replied 'I love you, wife. You stay well' and I said 'What are you talking about? We'll stay well together' and then the talking stopped," said Liu.

"The baby cried for an hour and then there was no voice."

Cranes, drills, ladders, sniffer dogs and life detection equipment are being used to locate those trapped, but emergency workers and soldiers have also had to shore up the ruins to avoid further tragedies.

Rescuers are set to start using diggers and extractors to remove giant concrete slabs once they have ensured all residents from the upper parts of the rubble have been freed.

The quake struck on the weekend before Chinese New Year when many relatives would have joined families in the complex to enjoy the holidays.

Now they endure an agonising wait for news.