Police officers in Hong Kong stormed enclosed railway stations on Sunday, firing tear gas in an effort to force out protesters.

One video inside Tai Koo station showed officers firing what appeared to be non-lethal ammunition at close range.

It also showed several police beating people with batons on an escalator.

In the bustling central Wan Chai district, petrol bombs and bricks were thrown at police, who responded by charging at protesters.

A number of people, including a police officer, were injured in the clashes.

The protesters have started to adopt new tactics, striking in multiple areas in smaller groups before running when the police arrive, says the BBC's Stephen McDonell who is in the city.

Hong Kong's mass demonstrations and unrest show no sign of abating, more than two months after they were sparked by a controversial extradition bill.