According to Emergency_In_SF, "Bomb threat at Pier 96 [home to Norcal's Recycle Central] resulting in evacuation of 100+ people. No other info available yet." (Posted at 3:38 p.m.)
We'll update as soon as we know more.
Update 5 p.m.: Emergency_In_SF reports, "Walk through of Pier 96 has been completed. No bomb found. Area is safe."