Hong Kong police have violently tackled suspected protesters with batons and using pepper spray on a train in the city’s subway after thousands of people marched on the street in defiance of a ban.
Police say they were called to the scene amid violence against citizens by “radical protesters”.
However, it is unclear if all those injured and arrested in the subway system were involved in demonstrations.
Protesters took to the streets on August 31 to mark the fifth anniversary of China’s government banning fully democratic elections in Hong Kong.
They lit fires, threw petrol bombs and attacked the parliament building.
In response, riot police used tear gas, rubber bullets and water cannon to disperse crowds, and fired live warning shots as they tried to clear the streets.
The latest protests came just a day after the arrest of several key pro-democracy activists and lawmakers in China’s special administrative region.
Hong Kong has now seen 13 successive weeks of demonstrations.
The movement grew out of rallies against a controversial extradition bill – now suspended – which would have allowed criminal suspects to be sent to mainland China for trial.
It has since become a broader pro-democracy movement in which clashes have grown more violent.
During protests, crowds gathered by Prince Edward and Mong Kok stations in Hong Kong’s Kowloon neighborhood.
Police said in a tweet they had responded at both sites after reports of “radical protesters” assaulting citizens and damaging property.
In a statement, Hong Kong’s government also said some protesters had “committed arson and “hurled miscellaneous objects and iron railings” on to railway tracks, “completely disregarding the safety of other passengers”.
Forty people were subsequently arrested for unlawful assembly, criminal damage and the assault of police officers, police spokesperson Yolanda Yu told reporters.
However, several people complained of excessive force used by the authorities.
MTR, which operates the city’s subway line, told local media that three stations – Prince Edward, Mongkok and Kowloon Bay – had been closed as a result of the incident.
Protesters took to the streets in the Wan Chai district, many joining a Christian march, while others demonstrated in the Causeway Bay shopping district in the pouring rain. Many carried umbrellas and wore face masks.