Salvos of tear gas Thursday heralded the start of Hong Kong’s fourth day of continuous, territory-wide unrest and transport disruption as anti-government protesters escalated their efforts to force political concessions from the Beijing-backed government. Students also erected defenses at university campuses, stockpiling homemade weapons, in anticipation of clashes with police. Early morning volleys of tear gas were fired near the Polytechnic University, where police came under attack from students armed with bows and arrows. Since Monday protesters have periodically barricaded the Cross Harbour Tunnel approach roads, which skirt by the campus, and last night set fire to tunnel toll booths.