I have been in Hong Kong for last couple of years and my visa expires in 1 weeks. 4 weeks ago I submitted my visa extension application however I still have not heard from immigration and my visa is expiring. Can I still stay in Hong Kong or I need to leave?

Its best to call the immigration officer to check your extension application status. Under normal circumstances, you are allowed to stay in Hong Kong until the extension application is approved even your current visa is expired.