Hong Kong police said they arrested three people in connection with arson and vandalism in Kowloon late Wednesday.
In a news release on Thursday morning, the police said three people - a 15-year-old girl, a 16-year-old boy and a 29-year-old man - were arrested in connection with vandalising public buses.
A fourth person escaped, police said.
According to police reports the four boarded buses, pressed the emergency buttons, then began smashing windows with hammers.
Police also said they received reports that five people threw petrol bombs at a Japanese restaurant on the street level of a shopping mall in Cheung Sha Wan. There were no reported injuries.
Police said several other people started a fire at a street junction in Mong Kok, an area that has regularly been the site of violent clashes between protesters and police during more than six months of social unrest in the Chinese-ruled city.
Police did not say the vandalism was connected to the protests.
Separately, the Hong Kong Football Club Rugby Section announced it has cancelled its annual rugby tens tournament, scheduled for next April, due to the unrest.
"Owing to the ongoing situation in Hong Kong, the tournament has, for the first time, had difficulty in attracting and securing firm commitments from enough overseas teams of sufficient quality," the football club said in a statement Thursday.
The tens tournament is traditionally played ahead of the Hong Kong Rugby Sevens, with both events drawing prominent names in the rugby world.