HONG KONG - A 25-year-old man was sentenced on Tuesday to 52 months in prison for violent acts including vandalizing police facilities with gasoline bombs.

Lucas Chong Yam-miu threw a gasoline bomb at a police vehicle outside the police headquarters in Wan Chai and another at a police station in Happy Valley on June 7 last year.

He was arrested in a North Point apartment on the same day. His resistance later at a police station left three officers injured.

Chong pleaded guilty to nine charges, including arson, possession of drugs, resisting officers, and offenses under the traffic ordinance.

District Court Judge Pang Chung-ping said a long prison term is warranted, given the severity of the case. Gasoline bombs are very dangerous, as their destructive power is difficult to control, and may hurt innocent people, Pang said.

Even though no one was injured in the attacks, the potential risk cannot be ignored, the judge added.

Pang described the case as a "direct attack on Hong Kong's rule of law". He said the court needs to protect frontline law enforcers and let the public know that such violence won't be tolerated.

The judge handed down a 52-month imprisonment and a fine of HK$5,000 (US$645) after taking into account Chong's mental condition, guilty plea, and no serious injuries in the incident.

Pang also said the case is not related to the anti-government protests stemming from the extradition bill incident since June 9 last year.

On Monday, 15 defendants appeared in court to face rioting charges for participating in a protest near the Hong Kong Polytechnic University on Nov 18 last year.

Three of them faced additional charges of possession of instruments fit for unlawful purposes. Two others were also charged with possessing offensive weapons.

The 13 men and two women, aged 16 to 61, including four students and one teacher, were released on bail till the next hearing scheduled for Aug 17, with 12 of the accused placed under a curfew.

They are among the more than 250 people facing charges connected to rioting during protests near and on PolyU's Hung Hom campus in late November.

On Friday, a 21-year-old lifeguard became the first protester to plead guilty to a rioting charge over the anti-government protests the began last year. He was sentenced to four years in prison for taking part in a protest outside the Legislative Council complex on June 12.