Thousands of demonstrators surrounded government buildings in Hong Kong on Sunday night, breathing new energy into an Occupy protest movement that seemed to be losing steam in recent weeks. Some observers said the crowds Sunday were the largest yet in more than two months of protests.

Video from the scene shows police using tear gas, pummeling the crowd with batons, and making several arrests.

The protesters — who have used umbrellas as shields, leading some to brand the movement as an "Umbrella Revolution" — gathered to take back Lung Wo Road, a street in Hong Kong where cops violently cleared away encampments last month.

The student-led protest movement began in late September after China reneged on a promise to hold free and open elections in Hong Kong in 2017. Hong Kong has been under Chinese control since 1997, when it was handed over from Britain after 150 years of colonial rule. A committee of pro-Beijing business tycoons has chosen Hong Kong's leaders since the transition.

Sunday night's demonstration followed a call from the Hong Kong Student Federation (HKSF) to step up action after a police crackdown and continued government refusal to meet with activists, the Epoch Times reported.

"I think we have made it very clear that if [the police] continue the violent clearing of the place, we will take further action," HKSF leader Yvonne Leung told the Epoch Times.

Student leaders said the demonstration was not intended to provoke a confrontation with police. The HKSF's official Twitter account asked participants to "stay calm, stay safe," during the gathering. But tensions quickly escalated, with police spraying tear gas yet again into the crowd.

Reuters described a chaotic scene where riot police wielding batons and shields charged at demonstrators, wrestling several people to the ground. Later in the evening, protesters reportedly hurled eggs, water bottles, and wooden boards at the cops, drawing blood and prompting officers to hit back with their batons.

Hong Kong citizens have formed a petition requesting the UN Commission on Human Rights investigate the ongoing police abuse of protesters, the Los Angeles Times reported. The petition, which began Friday, has already drawn more than 15,000 signatures. Amnesty International also warned the police Friday against using excessive force.

The protests had been diminishing in size until Sunday night, with police making dozens of arrests and forcibly clearing encampments in the city's Mong Kok district. Several thousand demonstrators remain encamped in the Admiralty and Causeway Bay districts.

Some protesters have responded to the aggressive police tactics by "strolling" in large groups through shopping centers for hours, the LA Times reported, with some carrying signs that read "I want free and fair elections." Protesters have also adopted the three-finger salute popularized by the Hunger Games movies, a gesture that has also been used by pro-democracy demonstrators in Thailand.