Hong Kong police say 13 officers were injured when protesters threw an unidentified liquid at them in a clash on Monday morning.
The injured officers were sent to hospital, according to a statement released by police.
Officers said a group of protesters had blocked the road and charged at a police cordon.
"Police officers at the scene were injured and among them, some experienced difficulty in breathing and had swollen and itchy skin. Thirteen officers were sent to the hospital for treatment. The case was taken up by the Organised Crime and Triad Bureau," the police statement read.
CNN's team on the ground saw police charging at protesters in the same incident.