As rescuers continue the grim task of digging bodies from the rubble of an apartment complex that collapsed in a Taiwan earthquake, anger is growing over the shoddy construction of the building and the island's questionable safety record.

The Wei-kuan building was the only high-rise to crumble completely in the 6.4 magnitude earthquake that shook the southern city of Tainan before dawn Saturday, with 61 confirmed dead so far, mostly from the complex.

More than 60 residents remain buried in the ruins and the chances of finding survivors are slim.

Prosecutors say there were "flaws" in the building as they question the developer and two associates on charges of professional negligence resulting in death.

Distraught relatives of residents told AFP they had complained over cracks in the walls of the building. Pictures from the disaster site show tin cans and foam were used as fillers inside the concrete.

Experts say that cost-cutting shortcuts have long dogged the construction industry in Taiwan.

"Because of competition, for a long period of time, the local construction industry has not been well managed," said Chern Jenn-chuan, civil engineering professor at National Taiwan University.

The disaster has struck a nerve with the public, increasingly embittered by a string of disasters, from food safety scandals to a water park explosion that left 15 dead.

"So-called competitiveness in Taiwan is all cost-oriented, so this kind of situation isn't a surprise at all," said a post on Taiwan's popular PTT online forum after the building collapse.

"They just collect the money and it's not their responsibility anymore," another user commented.

Prosecutors said there were too few steel reinforcing bars in parts of the building, and that the developer may have used a borrowed licence for the construction of the property.

Engineers helping at the rescue site added that some walls many have been knocked down on the ground floor, which housed part of a multi-storey electronics store.

"Apparently in this case, there were indeed flaws in the construction of the building," a court statement said Wednesday.

- 'Black-hearted developers' -

The Wei-kuan building had 96 apartments and was completed in 1994, before a new building code was brought in following a devastating earthquake that left 2,400 people dead in 1999.

Professor Chern said the disaster, which brought down buildings across the island, had led to better safety measures and awareness among developers.

"Many people now understand the grave responsibilities," he told AFP, adding the number of safety breaches had dropped.

The revised building code put in stricter requirements to make structures more quake-proof, including increasing the number and resilience of reinforcing bars.

But Max Lo, former president of the Taiwan Engineering and Science Association, says while newer buildings are structurally sound, not enough has been done about the ones built before 1999.

"Each county had identified the most notable at-risk buildings in its area, but they still haven't all been dealt with," he told AFP.

"Just because a building doesn't collapse after a quake, that doesn't mean it's okay," he added.

"It needs regular check-ups, like a human body. The government needs a complete set of policies to deal with such older, or higher-risk buildings as soon as possible."

The island's President-elect Tsai Ing-wen, who will take office in May, said she would prioritise building safety and review the resistance of older buildings to quakes and other disasters.

Meanwhile, the public is calling for maximum punishment for the developers -- particularly after scepticism over previous safety scandal cases.

Last year, food tycoon Wei Ying-chung was acquitted on charges of selling tainted cooking oil, prompting protests over his release.

There was also outrage when only one person was indicted after an explosion at a water park killed 15 and injured hundreds when clouds of multi-coloured corn starch sprayed on revellers ignited due to heat from the stage lights.

Victims have demanded prosecutors reopen the probe into that accident.

"I hope these black-hearted developers all get death sentences," said one PTT forum user in response to the Wei-kuan disaster.

"They killed so many people just for the sake of making money."