By Agence France-Presse
The crash happened on the island of Tsing Yi with images on local media showing the back half of the taxi completely crushed and part of the front of the coach sheared off.
A man and two women were declared dead at the scene and two died in hospital, police said.
Local media reports described the bus as a "tourist coach" but reported that it had been carrying workers to the airport.
Tsing Yi is connected by a freeway to Hong Kong International Airport on neighbouring Lantau island.
Television footage showed the injured being treated by the side of the road before they were taken to four hospitals.
The South China Morning Post reported that several of the injured were in serious condition.
One coach passenger said the bus had been travelling fast and had crashed into a stationary taxi with its hazard lights on at the side of the road, according to SCMP.