Clashes between anti-government protesters and police in Hong Kong broke out on Monday evening in Tuen Mun over a mysterious smell that led to accusations the force was testing chemicals at a facility, with the chaos ending in tear gas fired as vandals again targeted shops. Protesters had gathered outside Tai Hing Operational Base on Tsun Wen Road from 8.30pm, shining laser beams at a dozen officers on duty. Demonstrators also placed rubbish bins, signs and other items on roads to block traffic. At the gathering’s peak, hundreds of people were at the scene, shouting abuse at police. The assembly centred on an odd smell that residents claimed came from the police base earlier in the afternoon. Some alleged that the pungent fumes, which they said smelled like tear gas, could mean police were testing chemicals at the facility. The force denied the accusations in the evening. A spokesman said both police and fire services could not confirm the source of the smell. The fire service said it received 18 calls about the smell, between 3.30pm and 4.30pm. Two people on nearby Ming Kum Road were treated by ambulance staff, without being sent to hospital, after inhaling the mysterious gas and complaining of discomfort. At about 10.10pm, protesters smashed the glass screen of a Bank of China outlet nearby and a closed Lung Mun Cafe outlet operated by the Fulum Group, which protesters believe is linked to a Fujian clan. Police admit adopting more aggressive tactics in bid to quell rising violence A petrol bomb was also hurled into the shop, immediately starting a fire. On Thursday, a Lung Mun Cafe in Hung Hom was trashed by four masked men . That outlet is separately run by an operator who said he was on the side of protesters. The vandals had smashed windows, computers, surveillance cameras and furniture in his store. At about 10.20pm on Monday in Tuen Mun, police emerged from the base, firing multiple rounds of tear gas outside. Firefighters soon arrived to quickly put out the blaze at the cafe. After the initial dispersal, hundreds of protesters remained outside the police building as of 11.30pm, chanting protest slogans in a stand-off with officers. Before midnight, a man was arrested and taken into the police base. Democratic Party vice-chairman Lo Kin-hei said in a post on Twitter that a tear-gas canister entered the corridor of the seventh floor of Yat Sang House on Siu Hin Court estate. An accompanying clip in Lo’s tweet showed a smoke-filled corridor with the suspected canister on the ground. A resident expressed her anger over the police action to media. As of 12.30am on Tuesday, fewer than 100 protesters remained at the scene.