Police fired tear gas at a group of protesters marching toward the venue of the Group of 20 (G20) summit in the US city of Pittsburgh on Thursday afternoon, local sources said.

The march does not have a city permit and therefore has been declared by police as an unlawful assembly.

The incident occurred when leaders of the G20 were arriving in Pittsburgh for the two-day summit scheduled for Thursday and Friday, the third of its kind since the outbreak of the global financial and economic crisis last year.

TV footage run on major news networks showed a chaotic scene on the city streets, where riot police confronted the protesters defiant of the demonstration ban.

The police used cars to block the street to prevent the protesters from heading closer toward the summit venue. "If you donot disperse you may be subject to arrest or other police action, including actual physical removal," the police kept repeating the message through loud speakers as they fired tear gas.

The marchers seemed to have dispersed following the tear gas shots, which left some coughing and some others covering their faces with handkerchiefs or scarves.

Some of the protesters, however, rolled trash bins toward the police line or threw stones at police vehicles in return.

Local witnesses said that the number of protesters was between several hundred and a thousand.

According to earlier reports, the host city and the state of Pennsylvania have mobilized nearly 5,000 police, national guards and other law enforcement personnel for the security of the summit.

(Xinhua News Agency September 25, 2009)