from Shenzhen Bay pier to hongkong airport by bus

My questions are since i a, an indian passport holder:
1)I will not enter Hongkong city since my purpose is to take a flight from Hongkong airport.. do i need a transit visa in such a case ?
2) If needed, where will i get it..on arrival at Hongkong airport or at Shenzhen Bay pier or which place on enroute?
thanks in advance