Some demonstrators were carried away on stretchers after baton-wielding officers moved into a crowd in the Mong Kok district.
Police claimed they used "minimum force" as protesters "suddenly attempted to charge" their cordon lines.
However, activists say they were repeatedly hit with batons and did nothing to provoke the violence, as a senior politician said weeks of rallies had reached a "critical moment."
Demonstrators first took to the streets on Sept. 26 after China announced it would screen candidates running in Hong Kong's elections in 2017.
By Ruchi Singh
reporter
Park Sae-jin
swatchsjp@ajunews.com
