The victims have been transferred to local hospitals, although their conditions are not known, Hong Kong officials said.
A 60-year-old man has been arrested and accused of arson, Hong Kong police said at press conference Friday.
The man, whose last name is Cheung, was critically injured and told police he set the fire, authorities said.
Police said they believe the fire was an isolated incident carried out for personal reasons. There is no evidence it was terror-related, they said.