Observatory says low-pressure area has intensified into tropical depression and will enter within 800km of Hong Kong no later than Wednesday.

Observatory says low-pressure area has intensified into tropical depression and will enter within 800km of Hong Kong no later than Wednesday.

Circulation of tropical depression is relatively small and it will maintain a distance of about 300km or more from Hong Kong for most of Thursday, forecaster says.

Forecaster says it will issue the No 3 typhoon signal between 9am and 11am on Friday.