Typhoon Haima is posing a direct, substantial threat to Hong Kong and Signal No. 8 could be raised by forecasters early on Friday.
At 4.10 am, on Friday the Hong Kong Observatory said typhoon signal No 8 is expected to be issued at or before 6:30 am. Winds locally will strengthen further.
By 7 pm on Thursday, the storm had already caused at least 159 Hong Kong flights to be cancelled on Friday and disrupted sea traffic.
It said it would consider raising the No 8 signal on Friday morning.
Haima is the third severe typhoon to hit the city in October. The last time that happened in October was in 1989.