The red rainstorm warning was raised twice in three hours on Thursday amid widespread downpours across Hong Kong.
In issuing the red alert again at 12.40pm, the observatory said further heavy rain could cause serious road flooding and traffic congestion and that several areas in the New Territories were particularly being battered by downpours.
"Heavy rain is affecting the northern part of the New Territories, especially in Pat Heung and Kam Tin areas," it said.
"More than 60 millimetres of rainfall have been recorded in the past one hour.
"Residents in the northern New Territories, who are likely to be affected, are advised to take necessary precautions to avoid possible flood damage. Heavy rain may bring about flash floods. People should stay away from watercourses. They should also pay attention to the flood sirens if they are nearby."
The red rainstorm warning was replaced by an amber alert at 3.30pm.
"Locally, around 50 millimetres of rainfall were recorded over many places in the afternoon, and rainfall even exceeded 80 millimetres over parts of the New Territories West," the observatory said.
The forecaster had also issued an amber warning at 8.35am, before upgrading this to red an hour later.
The Drainage Services Department confirmed five incidents of flooding in the New Territories as of 3pm.
Two cases were reported along San Tin Highway near Mo Fan Heung, two on San Tin Tsuen Road, and one in Tai Wo Village, according to the department, which also dispatched more than 100 emergency response teams across the city.
According to the observatory's forecast, the remnant of tropical storm Danas was moving southwest across eastern Guangdong and might skirt Dongguan and Huizhou.
"The active southwest monsoon to its south will generally affect the vicinity of the Pearl River estuary [on Thursday and Friday]. There will be torrential rain and squally thunderstorms over the region," it said.
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Last updated: 2025-07-10 HKT 17:19