Young protesters, many wearing masks to disguise their identity, filled the open area of a Hong Kong shopping mall Sunday and folded paper "origami" cranes in the latest twist in a pro-democracy movement that has stretched into a fourth month.

They first 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.

Transit authorities closed the two stations on the airport express train to guard against a possible disruption of transportation to the transportation hub.

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 were also suspended. Passengers were advised to leave sufficient time to reach the airport.

The latest gathering came after a night of violent clashes in which the police used tear gas and rubber rounds against protesters who threw gasoline bombs toward them and set fires in streets.

The protests generally begin peacefully, but often degenerate into confrontations that hard-line protesters say is needed to get the government's attention.

Hong Kong's leader, Chief Executive Carrie Lam, has agreed to withdraw an extradition bill that first sparked the protests in June. But the anti-government protesters are pressing other demands, including fully democratic elections in the semi-autonomous Chinese city and an independent investigation of complaints about police violence during earlier demonstrations.

Protesters say Beijing and 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 Oct. 1 celebrations of its 70th anniversary in power. Hong Kong's government has canceled a fireworks display that day, citing concern for public safety.