Development minister Bernadette Linn said officials want to step up training of sewer workers to prevent incidents involving manholes.

Her comments came after the death of two workers last week at a manhole in Sha Tin, the same site where two others died nearly two decades ago.

Speaking on a TVB programme, Linn said the contracts state that workers should only operate on the ground, and if relevant works require them to enter the manhole, only qualified personnel are allowed and risk assessment must be conducted beforehand.

She also said officials are looking into adding clauses to future contracts, requiring workers who only conduct cleaning on the ground to go through training as well.

"If you do enter manholes [in future], you have to inform the Drainage Services Department beforehand and receive its approval," she said.

"We're considering making it mandatory for those doing the cleaning on the ground to also go through manhole training. This is to raise their awareness."

Separately, Linn said officials are considering whether to immediately prosecute homeowners found to have illegal structures, rather than issuing orders for removal.

The government has been reviewing the Buildings Ordinance after cases of unauthorised structures were reported.

The development secretary said the administration is studying whether the prosecution process can be streamlined, the prosecution threshold lowered and relevant fines raised.

She noted that a clause in the current legislation stipulates harsher penalties for offenders who "knowingly" violate the law. Linn said officials want to remove such wording, which she said allows homeowners to claim they were not aware of the illegal structures and that the problem had already existed before they bought the place.

But the minister said officials will make sure the relevant amendments – to be put forward in the final quarter of this year – will be reasonable.