Hong Kong police said Monday tear gas was deployed "87 times" in clashes with pro-democracy protesters on Sunday as they defended their controversial use of force against crowds in the usually stable city.

Assistant Commissioner Cheung Tak-keung said tear gas was used at nine different locations, although he did not clarify whether multiple canisters of gas were used on each occasion.

"The use of force is used in a situation when we have no other alternatives," he told a press conference, adding officers felt compelled to fire canisters when "police cordon lines were heavily charged by some protesters".