The Environmental Protection Department has advised people to reduce physical exertion and outdoor activities due to higher than normal pollution levels.
At 2pm today the Air Quality Health Index at some general and roadside stations reached 9 or above, corresponding to a "Very High" health risk.
Readings at Tuen Mun station reached 10+, corresponding to a "Serious" health risk.
The department said Hong Kong is being affected by the outer subsiding air of Typhoon Talim.
It warned the health index at more monitoring stations may reach the "Serious" level later today.
The Hong Kong Observatory said Typhoon Talim will intensify gradually and move northwest or west-northwest towards Zhejiang.
Pollution levels will remain higher than normal.
Children, the elderly and people with heart or respiratory illnesses are advised to reduce physical exertion and outdoor activities.
Click here for index readings.
