Before a flat is leased, estate agents must now check whether the building has illegal structures or is subject to repair orders.
The new rule extends the agents' duty to conduct a land search for a property when dealing with a purchase to cover leases as well.
It is contained in a practice circular issued by the Estate Agents Authority yesterday. The authority said the collapse of a 55-year-old building in To Kwa Wan in January had sparked concern about old tenements with illegal structures.
'As many tenants living in old buildings are from the grass roots, they may not be aware of the risks involved in renting such properties,' it said.
An agent should check whether any orders requiring demolition or alteration of illegal structures are registered and whether these orders have been complied with, and then inform the potential tenant.
Even when no such order had been issued, if there appeared to be illegal structures, the agent should alert the client, the authority said.
An agent who fails to comply will face disciplinary action ranging from an admonition to the loss of his or her licence, depending on the case.
