Beijing, Shanghai and Hong Kong in 7 days
Beijing, Shanghai, and Hong Kong are huge cities, and it may not be enough 7 days for each of them. That is why it is quite hard to visit them all in just 7 days, but it is possible. Though, you will have to spend those 7 days in a rush.
Days 1-3: Beijing: see Three days in Beijing.
Day 4: Beijing to Shanghai transportation: take airplane (2 hours travel time) or bullet train (5.5 hours travel time). Check Beijing-Shanghai transportation for more info. Which ever option you chose, make sure to start your trip early, so you could have half a day for Shanghai sightseeing.
Shanghai: When you arrive in Shanghai, check-in in you hotel/hostel, and rest a little bit. After that first visit Shanghai Old French Concession, then Shanghai World Financial Center in Pudong.
Day 5: Shanghai: see One day in Shanghai.
Day 6: Shanghai to Hong Kong transportation: take airplane (2.5 hours travel time). Check Shanghai-Hong Kong transportation for more info.
Hong Kong: When you arrive in Hong Kong, check-in in you hotel/hostel, and rest a little bit. Then visit attractions from One day in Hong Kong. Skip Temple Street Night Market, if you don’t have time to visit all attractions from One day.
Day 7: Hong Kong: do Day 3 in Hong Kong.