Police said the KMB bus was travelling on Ngau Tau Kok Road near Choi Wan Road and was suspected to have hit the 84-year old man as he was crossing the road.
He suffered serious head wounds and was declared dead at United Christian Hospital.
The driver was 38 years old.
The bus company said it will fully cooperate with the police investigation.
It expressed condolences to the family of the deceased.
The force urged witnesses to come forward.