Dozens of pro-democracy protesters were in a tense standoff Tuesday night with a large number of riot police near Hong Kong’s government headquarters.

Television stations showed hundreds of police wearing helmets and holding shields and batons facing off with student-led protesters, who have occupied key roads and streets in Hong Kong’s business district for more than two weeks. The two sides have been locked in a stalemate after the government called off negotiations last week.

It was not immediately clear what caused Tuesday night’s standoff, but local television reports said it began when police allegedly arrested a protester.

Some demonstrators then tried to take over a tunnel in front of the government headquarters near the entrance to the office of the city’s leader. The reports said police used pepper spray to try to disperse the protesters but failed and retreated, leaving the tunnel in the hands of the protesters, who were building new barricades to expand the occupied area.

Earlier Tuesday, police cleared barricades from the pro-democracy protest zones, signaling authorities’ growing impatience with the activists.

Appearing to use a strategy of gradually chipping away at the three main protest areas, hundreds of police fanned out in the early hours to take down barriers that the protesters had erected overnight. Officers used electric saws and bolt cutters to take down bamboo scaffolding built in the Admiralty area after a mob of masked men stormed some of the barricades the day before.

Police also removed metal barricades from another protest camp on a road in the nearby Causeway Bay shopping area to free up a lane for traffic.

Police will continue to take down barriers set up by protesters, spokesman Steve Hui said. He said officers arrested 23 men in Monday’s violent clashes, when masked men and taxi drivers led a crowd of several hundred who tried to charge the protest zone.

The police operations over the past two days follow the government’s abrupt cancellation of talks scheduled last Friday with the activists, citing the unlikelihood of a constructive outcome given their sharp differences.

The protesters want China’s government to drop plans for a pro-Beijing committee to screen candidates in the territory’s first direct elections, promised for 2017. They also demand that Hong Kong’s deeply unpopular Beijing-backed leader, Leung Chun-ying, resign.

Leung has said there is “almost zero chance” that China’s government will change its rules for the 2017 election.

The demonstrations have posed an unprecedented challenge to the government. Organizers say as many as 200,000 people thronged the streets for peaceful sit-ins after police used tear gas on Sept. 28 to disperse unarmed protesters.

Numbers have since dwindled and the remaining demonstrators, sensing that the earlier actions were aimed at testing their defenses, braced Tuesday evening for possible further police moves to clear out their protest camps.

Beijing is eager to end the protests to avoid emboldening activists and others on the mainland seen as a threat to the Communist Party’s monopoly on power.

(AP)