At 9:03 a.m. on September 11th 2001, five hijackers crashed United Airlines Flight 175 into the World Trade Center's South Tower. The tower collapsed at 9:59 a.m. after burning for 56 minutes. After impact, one stairwell remained intact, allowing 18 people to escape from above the impact point. 630 people died, fewer than half the number killed in the North Tower. Casualties in the South Tower were significantly reduced because some occupants started evacuating when the North Tower was struck.