Chief Executive John Lee said on Tuesday that officials are looking into improving the city's drainage system and how to better alert the public to massive storms, after torrential downpours brought havoc to Hong Kong last Friday.

What was described as a "once in 500 years" rainstorm triggered floods and landslides across the city. Parts of Hong Kong were also flooded on Monday after more than 100 millimetres of hourly rainfall.

Ahead of his weekly Executive Council meeting, the CE said Monday's concentrated heavy rainfall did not meet the criteria for issuing a black rainstorm warning, but authorities quickly responded to the flooding that ensued.

Lee said the Drainage Services Department will step up patrols at rivers and watercourses, and clear debris to minimise the chance of flooding.

The government is planning drainage enhancement work across the territory, with priority given to places with a higher risk of flooding, he added.

"We have reduced the flooding black spots from over 100 to what now remain as four. That means we have a continued exercise to reduce the risk of flooding. We will continue to do that, and already the Secretary for Development has informed the public that the relevant department is doing a long-term examination on how this should be done. The review will probably finish some time next year," he said.

The CE also said public servants worked around the clock to respond to the aftermath of Friday's rainstorm, but more has to be done to inform people about such serious situations.

"Despite the limitations by science, we still have to think of other ways of helping people to get to know more information earlier and in bigger detail," he said.

"I think if we think more from the citizens' angle – where and what they want to make preparations – we can improve the alert system. This is what I have asked the government to do and we'll look at it seriously."

Lee said more than 45 counters would be in service on Tuesday and Wednesday to help people affected by the rainstorm and the recent Super Typhoon Saola apply for emergency relief funds.

Local farmers, fish farmers and fishermen who suffered serious losses can also register for financial assistance until September 20.