The Observatory issued the black rainstorm warning at 11:45pm on Monday, warning of possible flooding as heavy downpours lashed parts of Hong Kong. The second red rainstorm warning of the day was issued earlier at 10.35pm.

"Rain is particularly heavy in Kwai Tsing and Sha Tin districts. It may cause serious flooding. Residents who are likely to be affected are advised to take necessary precautions to avoid possible flood damage," the forecaster said.

"Heavy rain of more than 70 millimetres of hourly rainfall has fallen or is expected to fall in the above regions."

Monday's first red rainstorm alert was in effect from 12.20pm and lasted for an hour, while the amber warning was in force on four separate occasions.