Taiwan prosecutors were on Wednesday questioning the developer of an apartment complex that collapsed during an earthquake as prosecutors detailed flaws in construction of the building where nearly 100 people remain trapped.

Prosecutors in the southern city of Tainan have launched an investigation into Saturday's disaster after photos showed cans and foam had been used to fill parts of the complex's concrete framework.

The district court took the developer, identified as Lin Ming-hui, and two other people into formal custody late on Tuesday after they were grilled initially at the prosecutors' office.

So far 43 people have been confirmed dead and 95 are still missing after the collapse of the 16-storey Wei-kuan building.

It was the only high-rise in Tainan to crumble completely when the 6.4 magnitude quake struck before dawn on Saturday.

The three were taken into formal custody on charges of professional negligence resulting in death.

"The suspects are being questioned further today, but as it is underway, details are not likely to be made public," Tainan court spokeswoman Kuo Jen-shiow told AFP on Wednesday while the prosecutors were not immediately available for comment.

The other two suspects were Chang Kui-pao and Cheng Chin-kui, who some local media said were architects while others said they were employees of Lin's firm.

'Flaws in construction'  

According to a statement released by the court, prosecutors found the beams and pillars of the first five floors on the east side of the building had too few steel bars, and the bars were thinner than they were supposed to be.

It said samples taken from the third floor of the site also showed that the main steel bars were shorter than required.

"Apparently in this case, there were indeed flaws in the construction of the building," it said.

Rescuers were using diggers and other heavy equipment to remove giant concrete slabs to access the deeper layers of rubble where scores of people are feared buried.

The 72-hour "golden window" for finding survivors passed early Tuesday but near midnight, Tainan mayor William Lai offered fresh hope after rescuers detected signs of life.

"After detecting signs of life, the rescue team then banged in the direction of the signs three times, and they got a response three times. This shows there's a living person within," the mayor told a press conference.

But more than 10 hours later, the person has not been pulled out.

Some 175 people have already been rescued, including an eight-year-old girl and three others pulled from the rubble on Monday.

Cranes, drills, ladders, sniffer dogs and life detection equipment are being used to locate those buried, with emergency workers and soldiers shoring up the rubble to avoid further collapses.

The weekend quake struck two days before Lunar New Year, when many people would have been visiting relatives for the biggest celebration of the Chinese calendar.