Hong Kong Coalition secretary-general Tam Yiu-chung said on Saturday the Legislative Council should monitor the government without "overstepping boundaries" and not try to replace government departments.

His call came after the director of the Hong Kong and Macao Affairs Office, Xia Baolong, urged the city to improve its executive-led governance model, which he says the legislature and judiciary should support.

Speaking on a TV programme, Tam said Beijing's hope is for the three branches of government to co-operate and work towards the same goal.

"The branches should work together within the same framework, avoiding mutual attacks and smear campaigns. They should be actively supporting and co-operating with each other throughout the process," he said.

"Monitoring still exists in the system, but Legco must not overstep its boundaries – which is replacing the executive branch.

"Monitoring should be in the form of offering suggestions to the executive branch on how to make improvements."

Lawmakers are okay to vote against bills, Tam pointed out, citing the voting down of a government proposal to introduce a framework recognising same-sex partnerships in Hong Kong in September.

As for whether Legco can invoke the Powers and Privileges Ordinance as a way to oversee the government, he said caution was needed when exercising the power and only after thorough consideration.

"If the executive branch has already initiated an investigation or multiple investigations, does the legislature need to use the ordinance to initiate its own probe? We must assess whether this approach is necessary," Tam said.

He cited as an example the multiple probes initiated into the Tai Po fire disaster in November, saying it would be redundant if the legislature mounted its own investigation.