Hong Kong police have violently tackled suspected protesters after thousands marched in the city in defiance of a ban.
Images show police hitting people with batons and using pepper spray on a train in Hong Kong’s underground metro.
Police said 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 metro system were involved in demonstrations.
Thousands of people took to the streets on Saturday to mark the fifth anniversary of China’s government banning full democratic elections in Hong Kong.
Protesters lit fires, threw petrol bombs and attacked the parliament building.
In response, 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 neighbourhood.
Police said in a tweet that they 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” onto railway tracks, “completely disregarding the safety of other passengers”.
Police Yolanda Yu told reporters that 40 people were subsequently arrested for unlawful assembly, criminal damage and the assault of police officers.
But several people have complained about the excessive force used by authorities.
“The train stopped. Police boarded and hit me twice with a baton,” an unnamed man told the South China Morning Post newspaper.
“They didn’t arrest me. They were just venting their anger by hitting me,” he added.
MTR, which operates the city’s metro line, told local media that three stations – Prince Edward, Mongkok and Kowloon Bay – had been closed as a result of the incident. It is unclear when they will reopen.