Karachi- At least three participants of a Pakistan Tehreek-e-Insaf (PTI) sit-in being staged here were injured after the roof of a police check post, they had climbed on, gave in under their load. The mishap came to pass after too many PTI protestors, only to have a better view, got on the roof of a police check post, which foundered with a thud within minutes. The rescuers pulled the injured out of the rubble after breaking the doors or the post. The casualties were later rushed the casualties to the hospital. PTI Karachi is staging a demo at Schon Circle in solidarity with the party's week-long protest in Islamabad. Chairman PTI Imran Khan, has led thousands of supporters/demonstrating outside the legislature this week calling for Prime Minister Nawaz Sharif to go.