Authorities said a motorbike heading south on Tseung Kwan O Road was forced to stop because of traffic conditions, but the six cars behind it failed to brake in time.
The smash happened at around 7.40am.
The motorcyclist and three taxi drivers were injured and were taken to United Christian Hospital in a conscious state, while the drivers of three private cars involved in the collision didn’t require hospitalisation.
The accident led to congestion in the Tseung Kwan O Tunnel, with traffic backing up to Wan Po Road near Pak Sing Kok.
Separately, a man was killed in Central in a suspected hit-and-run.
He was found lying near the intersection of Possession Street and Queen’s Road West at around 4:30am.