An engineer on Thursday called the collapse of the tower crane on Anderson Road in Sau Mau Ping “a mystery”, noting it had been in use for a month and was not bearing any weight when it tipped over.

The accident killed three workers on the construction site on Wednesday, including the operator of the crane.

Speaking on an RTHK programme, Joseph Chi, chairman of the Hong Kong Institution of Engineers’ safety specialist committee, said it appeared that the welding of the base was not strong enough.

“From images online and close-up photos published in the media, it looks like the welding was not very sufficient, and had caused the structure to fracture,” he said.

But he added that one must examine the structural design before concluding whether it was the cause of the accident or whether other defects were to blame.

He said it’s strange for the structure to snap when it wasn’t lifting anything, a month after it’s been put in use.

When asked if the problem could’ve been identified earlier, Chi said some structural failures happen suddenly without any signs.

As for the government’s decision to inspect all tower cranes in Hong Kong, Chi said authorities should check if any of them had been lifting more weight than they could bear.