Hong Kong (CNN) Police fired tear gas and rubber bullets at protesters in Hong Kong on Wednesday, hours after tens of thousands of mostly young people surrounded the city's government headquarters and postponed the debate over a controversial bill that would allow fugitives to be extradited to China.

As violent clashes erupted between protesters and the authorities late Wednesday afternoon local time, Hong Kong Police Commissioner Steven Lo Wai-chung said the demonstration was being considered a "riot."

Rubber bullets, pepper spray and hand-thrown tear gas were used to push back protesters who had occupied the city's main thoroughfare near the government headquarters, as well as the roads around it, Lo confirmed.

He added that police had been left with "no choice but to start to use force."

Ambulances were seen rushing towards Harcourt Road, the main site of Wednesday's protest, amid reports of people being removed from the scene on stretchers. Lo said the number of officers injured was still being tallied.

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