It said winds would strengthen further due to the combined effect of tropical storm Lionrock and the northeast monsoon.
The Observatory also warned of gales over offshore waters and storm force winds on high ground over the south-western part of Hong Kong.
The MTR says rail and MTR bus services will remain as normal, while the Education Bureau says classes of all day schools are suspended.
The strong wind signal number 3 has been force since 4.40 am on Friday with gusts and rain from Lionrock battering Hong Kong. On Friday morning, one worker died after scaffolding collapsed in Happy Valley.