Hong Kong police are searching for six people believed to have lit a fire outside a government office in Kowloon early on Tuesday morning.
Officers seized shards of glass and plastic and glass bottles containing an unknown liquid, suspecting petrol bombs were thrown. The shutters of Lai Chi Kok government offices were blackened.
Six people dressed in black clothing and wearing hoods were believed to be involved in the case.
No one was injured in the incident and no arrests had been made, according to a statement released by police around 4am.
Police were uncertain whether this case was related to the ongoing anti-government protests in Hong Kong, which have gripped the city for more than six months, during which petrol bombs have frequently been thrown.
The mass demonstrations were triggered by the now-withdrawn extradition bill that could have led to fugitives being sent to face trial in mainland China, among other jurisdictions with which Hong Kong had no existing agreement.
In a night of violence on October 20, protesters threw more than 100 petrol bombs and damaged 11 MTR station entrances.
Authorities seized more than 3,800 petrol bombs from Polytechnic University in Hung Hom in November after the campus was turned into a stronghold for radical protesters during a two-week battle with police.