Agencies— Hong Kong police have violently tackled suspected protesters after thousands of people 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 metro.

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 metro system were involved in demonstrations.

People took to the streets on Saturday to mark the fifth anniversary of China's government banning fully democratic elections in Hong Kong.

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.

What happened in the metro?

During protests, crowds gathered by Prince Edward and Mong Kok stations in Hong Kong's Kowloon neighbourhood.

Police said in a tweet they had responded at both sites after reports of "radical protesters" assaulting citizens and damaging property.

Forty people were subsequently arrested for unlawful assembly, criminal damage and the assault of police officers, police spokesperson Yolanda Yu told reporters.

But several people complained of excessive force used by the 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."

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.