Scaffolding nets must be sampled on-site and pass safety tests by designated laboratories before they can be installed on building facades in future, the government announced on Thursday, as authorities set out new requirements to ensure the materials are up to standard.

Secretary for Development Bernadette Linn said officials are expecting a surge in demand for testing in Hong Kong and they are searching for suitable facilities to assist with such work.

"My understanding is that not many laboratories offer this service, because there's no market," Linn told reporters.

"We are right now contacting a number of laboratories, letting them know our new requirements, and seeing if they can gear up their facilities and manpower to provide this service."

Authorities said contractors must sample every batch of coverings on-site to be sent for screening with the whole process recorded on video, and the materials could only be installed if all samples passed the tests.

Other than undergoing safety tests, it would be mandatory for contractors to provide fire-retardant certification obtained from suppliers. Officials would also conduct spot checks after the nets have been put up.

The new measures came after non-fire-retardant nets might have aided the rapid spread of the blaze at Wang Fuk Court that claimed at least 160 lives, and that scaffolding coverings from hundreds of premises across the city had been removed under a government order.

Linn said authorities were aiming to have the first batch of approved materials put up in a month, while the Construction Industry Council has offered to help with mass procurement and testing services in the interim.

The minister also defended the construction industry in response to a lawmaker who said the sector "couldn't get any worse" following a number of emerging issues within the trade.

"Unfortunately, we see that there are indeed individuals in the industry not following the rules, whom I would call the black sheep. But we shouldn't blame a whole group of people for the mistakes of a few," she said.

"We can see that the entire construction industry is united and wants to do their job well, so we shouldn't sell ourselves short."

On the possibility of adopting metal scaffolding, Linn said the industry believes there should not be a sweeping approach and it would be necessary to identify sites suitable for the switch.