PITTSBURGH, Pennsylvania, (AFP) - Thousands of people peacefully demonstrated during the G20 summit in Pittsburgh, but police reportedly arrested 40 as they clashed with a smaller group late Friday. Waving banners and chanting slogans, protesters on Friday flooded into city streets lined with police in full riot gear, still tense after violent anti-G20 protests in the eastern US city late Thursday. New clashes erupted late Friday on the University of Pittsburgh campus, where police dispersed a crowd of around 400 with pepper spray and a noise device that emits an ear-splitting sound, a local newspaper reported. Around 40 protesters were arrested, according to the Pittsburgh Post-Gazette newspaper. The G20 summits routinely attract crowds of activists for scores of causes as well as anarchists opposed to what they see as inhumane free market policies. The earlier, larger demonstration took place without any incident. Security forces in Pittsburgh said there were up to 4,500 marchers, but Peter Shell, president of the Thomas Merton Centre which helped organize the march, estimated the number at twice that. It was the biggest protest march in Pittsburgh since the 1970s protests against Vietnam, Shell told AFP. As the marchers massed at the top of Fifth Avenue, a riot policeman rapped his baton hard against his shinguards, making a hollow thud with every tap. Mothers carrying infants, people walking their dogs, couples holding hands and entire groups waving flags and holding banners marched in the shadows of skyscrapers built for large corporations, turning the streets of Pittsburgh into a palette of protest messages of every colour. One group chanted Money for children, not for war, while pro-Tibet demonstrators chanted Stop the genocide. Members of the Falun Gong religious group marched in silence, bringing up the rear of the march. We came here to protest the Chinese regime and let people know about the persecution of Falun Gong, said Kwi Hwang, who says he was forced to work as slave labour, shelling pistachio nuts, making cane chairs and plastic flowers, while he served a five-year jail term in China for my beliefs. When I came to America, I saw the things I made as a slave in a Big Lots store, he said with a wry smile as he put a human face on one of the chief gripes of the anti-G20 protests. A young woman chanted at police as she passed: Youre sexy, youre cute, take off that riot suit. A youth who tried to cross the police line to hug a bystander was brusquely pushed back by a riot policeman. Dont do that again, the police officer said sternly. Sixty-six people were arrested, shops and businesses in the university area were vandalised, and at least six people were injured during Thursdays hours-long spree of violence. The black-clad, masked anarchists who fought running battles with police Thursday drew inspiration from previous demonstrations at global summits, including the G20 London meeting summit in April, where one bystander died after being hit by police. Ben Kopp, 20, who had travelled from Connecticut to be at the march, was a bit apprehensive but determined to get his own message to the leaders of the G20 nations - that they should stop taking advantage of people to achieve their economic goals. Im a little nervous, he told AFP as he crossed the Seventh Street bridge, which like the rest of the route was thick with riot police, on the final straight of the march. Id rather not get teargassed but when you think of the millions of people who go hungry every day around the world, a little bit of tear gas would be worth it, if we can made ourselves heard, he said.