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

Sunday'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.

Police used tear gas as they tried to advance on the protesters.

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

Transit authorities closed the two intermediate stations on the airport express train to guard against a possible disruption of transportation to the transportation hub. Separately an afternoon protest has been called at a shopping mall in the outlying Shatin district.

The Hong Kong International Airport Authority said that the train would operate only between the airport and the terminus station in the center of the city on Sunday. Some airport bus routes have also been suspended. The anti-government protesters are making several demands including fully democratic elections in the semi-autonomous Chinese city.