 On Collins and Russell Streets, barricades were ripped down and pushed at riot police who were called in to help quell the situation.A militant group of protesters known as the Arterial Bloc, dressed in white clothing with hoods covering their faces, collected industrial bins and dumpsters and used Melbourne's tram tracks to slide them into barricades and police, resulting in minor injuries to several police, the most serious being a broken wrist.At one stage a police riot truck was attacked with its windows smashed.