We need a taxi from Mui Wo (Lantau) to hong kong airport at 4am in the morning.

Oh, after arriving, you will find many taxies at the airport. It's easy for you to get one. So it's not necessary for you to book one in advance. It costs CNY 150 to 160. And it takes around 35 mins on the way.

Or you can take bus no.N35 at Airport (Passenger Terminal Building), and get off at Mui Wo Ferry Pier directly. It takes around 65 mins on the way. And the ticket fare is 21 HKD per adult. This bus only has two schedules every day: 01:30 and 04:30. Just hurry up and try to catch the second one.