Massive explosions rocked downtown Beirut on Tuesday, flattening much of the port, damaging buildings and blowing out windows and doors as a giant mushroom cloud rose above the capital. Witnesses saw many people injured by flying glass and debris Miles from the scene of the blast, balconies were knocked down, ceiling collapsed and windows were shattered.The cause of the blast was not immediately clear. It came at a time when Lebanon is passing through its worst economic and financial crisis in decades.