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

Key points: Some protesters took turns walking over the flag and spraying it with paint

Some protesters took turns walking over the flag and spraying it with paint One group of protesters trashed the subway station attached to the mall

One group of protesters trashed the subway station attached to the mall Hardliners in the pro-democracy movement say extreme actions are necessary

The day's action began peacefully, as protesters filled a shopping mall and, in a new twist, folded paper origami cranes that they tied onto a large rigging that they assembled in the mall in the Shatin district.

Some put a Chinese flag on the floor and took turns running over it, before defacing it and putting it in a dumpster outside, which they then pushed into a nearby river.

One group later attacked the Shatin subway station, which is connected to the mall.

Protesters sprayed the flag with paint after trampling it in the mall. ( AP: Kin Cheung )

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 grill 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.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 55 seconds 55 s Protesters lit a fire near the mall and subway station. (Photo: AP/Vincent Yu)

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

Protests started out peacefully

The protests began with an origami display, before turning violent later in the day. ( AP: Kin Cheung )

Hong Kong's pro-democracy protests, now in their fourth month, have often descended into violence late in the day and at night.

A hardcore group of protesters says the extreme actions are needed to get the Government's attention.

On Saturday night, police used tear gas and rubber rounds against protesters who threw gasoline bombs toward them and set fires in streets.

Before making the origami cranes, protesters at the Shatin New Town Plaza mall chanted slogans and sang a song that has become their anthem, backed by a small group playing on woodwind and brass instruments through their masks.

Many lined the balustrades of the three higher floors overlooking where others gathered in the wide space below.

Hong Kong's leader, Chief Executive Carrie Lam, has agreed to withdraw an extradition bill that sparked the protests in June.

Protesters poured cooking oil and scattered debris near the entrance of the subway station after police arrived. ( AP: Vincent Yu )

But the anti-government protesters are pressing other demands, including fully democratic elections in the semiautonomous Chinese territory and an independent investigation of complaints about police violence during earlier demonstrations.

Protesters say Beijing and Ms Lam's government are eroding the "high degree of autonomy" and Western-style civil liberties promised to the former British colony when it was returned to China in 1997.

The unending protests are an embarrassment for China's Communist Party ahead of October 1 celebrations of its 70th anniversary in power. Hong Kong's government has cancelled a fireworks display that day, citing concern for public safety.

AP