Snapped wires may have led to Monday's National Art Gallery crane accident which killed two workers, said Acting Manpower Minister Tan Chuan-Jin.
Calling it a "serious incident" after a visit to the construction site along St Andrew's Road yesterday, he added that it was still too early to say what actually happened.
It appears that there had been "nothing unusual" with the operation of the crane, and the weight of the excavator it had been lifting was well within limits.
"So the next step really is to determine what exactly happened - is it technical in nature, is it a systemic problem - so that lessons can be learnt, rectifications can be made," explained Mr Tan. "Not just here, but whether there are lessons for the industry as well."
The Manpower Ministry has ordered work at the site to be stopped for its investigations.
Project director Hideki Izumi, who works for the main contractor Takenaka-Singapore Piling Joint Venture, said the worksite's tower cranes, which were leased from Waheguru, were inspected monthly even though the industry norm is once every three months.
The crane, the boom of which collapsed at the Coleman Street site on Monday morning, was last inspected on Sept 19.
Its concrete counterweights fell too, crashing through scaffolding and killing a worker. Another died after being hit by the crane's hook assembly.
The bodies of Thai national Somkhot Chanyut, 50, who worked for Yong Nam Engineering, and Takenaka Corporation employee Ronju Ahmed, a 30-year-old from Bangladesh, will be flown back today.
Mr Tan sent his condolences to the families of the dead, and wished the two Bangladeshis and two Chinese nationals who were injured a speedy recovery.
While two of them have been discharged, Chinese national Gu Sheng Hui, 43, remains in the intensive care unit at Singapore General Hospital (SGH) after suffering head injuries.
Bangladeshi worker Imran Hasan Ahsan Ullah, 24, underwent a seven-hour surgery at SGH yesterday afternoon. "In the morning he could talk but he said his head was still paining, he's still not sure what happened," said his cousin Gani Islam.
This was the second crane- related incident at the site where the former City Hall and Supreme Court buildings are being turned into the National Art Gallery.
In July, a crawler crane's jib snapped and fell onto the road, but no one was hurt. But Mr Tan stressed that the incidents "were very different in nature".
There have been at least 15 deaths in the construction sector this year, but these were the first crane-related ones. There were five crane-related deaths last year and six in 2011.
Last Thursday, a worker also fell to his death at the Silversea condominium project when scaffolding beneath him collapsed. Four days earlier, another worker died when a tree fell onto the excavator he was operating.
Asked if the string of incidents was cause for alarm, Mr Tan noted that they were unrelated, adding that first "we need to investigate what exactly happened".
As for the suggestion that an industry labour crunch may have overstretched workers, he said such speculation was "not necessarily very helpful".
"We are mindful that obviously there is a tightening in the labour market, but safety measures need to be kept, regardless."