Hong Kong: Hong Kong’s corruption watchdog has arrested 21 government contractors for running suspected fake tests on concrete used to build a multi-billion-dollar bridge that will connect the city with Macau and mainland China.

The controversial project — described as a “white elephant” by its critics — has already suffered building delays, pushing back its opening date from 2016 to late 2017, while multiple workers have been killed in construction-related accidents.

Authorities in the southern Chinese city said on Wednesday they have asked for “comprehensive examinations” to “ascertain that the strength of concrete would meet the contract requirements”.

“In view of the seriousness of the matter, relevant departments will follow up this matter seriously so as to ensure that the quality of the works meets the required standards,” a government statement said.

The Independent Commission Against Corruption (ICAC) on Tuesday announced the arrests of 21 contractors including two senior executives, laboratory technicians and assistants in connection with the suspected fake tests.

The contractors worked with the Civil Engineering and Development Department to conduct compression tests on the concrete used for the nearly 50-kilometre long bridge since 2013, the ICAC said.

“The site laboratory technicians and laboratory assistants might have adjusted the times on the testing machines to cover up the irregularities,” the watchdog said in a statement, adding that the malpractice could have started in early 2015.

“During the ICAC operation, it was further revealed that some of the laboratory staff might have replaced the concrete samples by using a metal calibration cylinder and/or high strength concrete cubes to falsify the tests, so that the tests would appear to have been conducted properly.”