Protesters in Hong Kong trampled a Chinese flag, vandalised a subway station and set a fire across a wide street on Sunday as pro-democracy demonstrations took a violent turn once again.

The day’s action began peacefully as protesters filled a shopping mall in the Sha Tin district and made a large display of folded paper origami cranes.

Some put a Chinese flag on the floor and took turns running over it, before defacing it and throwing it into a river.

One group later attacked the Sha Tin subway station, which is connected to the mall. They jumped up to smash overhead surveillance cameras, used hammers to knock ticket sensors off gates and spray-painted and broke the screens of ticket machines, using umbrellas to shield their identities.

Riot police arrived following the attack and guarded the station after it was closed, with a metal grille pulled down to block entry.

Protesters then built a barricade across a street near the mall, piled what appeared to be brown palm fronds on top and set them on fire.

Police fired teargas as they tried to advance on the protesters, who had retreated before taking a position behind a wall of umbrellas held by those in the front.

Hong Kong’s pro-democracy protests, now in their fourth month, have often descended into violence late in the day and at night. A hard core of protesters say extreme actions are needed to get the government’s attention. On Saturday night, police used teargas and rubber rounds against protesters, who threw petrol bombs towards them and set fires in the streets.