HONG KONG- Hong Kong police stormed a shopping mall where a pro-democracy protest turned violent on Sunday, and activists trashed fittings at the rail station next door.

Hundreds of protesters, young and old, gathered in the mall in the New Territories town of Sha Tin, chanting: "Fight for freedom" and "Liberate Hong Kong."

Protesters also called for a boycott of businesses in the Chinese-ruled city seen as pro-Beijing and made a paper chain of receipts from those stores, which were then hung across the mall.

Activists rounded on a man believed to have opposed them when they had damaged the Chinese flag. Shouting, they pushed him into a corner beside the station and cheered as crowds punched and kicked him.

After 20 minutes, he managed to walk away, dazed and bleeding from the forehead. Protesters also smashed video cameras and ticket booths in the station.

Some started to trash fittings at the entrance of the mall itself. The protesters spilled outside where they lit barricades made of cardboard, broken palm trees and other debris.

Police warned they would fire tear gas.

Violence has hit parts of the former British colony at different times over more than three months, but life goes on as normal for most people most of the time.

However, pictures of petrol bombs and street clashes broadcast worldwide present a huge embarrassment for Beijing just days ahead of the 70th anniversary of the founding of the People's Republic on Oct. 1.

The Hong Kong government has already called off a big fireworks display to mark the day in case of further clashes. China, which has a People's Liberation Army garrison in Hong Kong, has said it has faith in Hong Kong leader Carrie Lam to solve the crisis.

There was also a noisy standoff between protesters and police at the Tsing Yi interchange station, which serves the Airport Express and the metro, which had been closed due to plans to block roads around the station.

Police fired tear gas to disperse protesters who threw petrol bombs in two new towns on Saturday after pro-China groups pulled down some anti-government graffiti. There were violent clashes elsewhere in the city.

Police condemned the violence and said there had been many serious injuries in clashes between people of "different views".

The protesters are angry about what they see as creeping Chinese interference in Hong Kong, which returned to China in 1997 under a "one country, two systems" formula intended to guarantee freedoms that are not enjoyed on the mainland.

China says it is committed to the arrangement and denies meddling. It has accused foreign governments including the United States and Britain of inciting the unrest.

Hong Kong police earlier prevented a protest targeting the airport.

Pro-democracy protesters have targeted the airport before, occupying the arrivals hall, blocking approach roads and setting street fires in the nearby town of Tung Chung.

(Reporting by Poppy McPherson, Jessie Pang, Farah Master, Felix Tam and Twinnie Siu Writing by Nick Macfie Editing by Giles Elgood) ((farah.master@thomsonreuters.com; +852 96318262 ;))