The male, whose age is unknown, locked himself in a building in the 2000 block of California Street at about 3:15 p.m., Sgt. Michael Andraychak said.
Andraychak said the male is believed to have a weapon, but poses a danger to himself only.
Police have closed California Street between Octavia and Laguna streets, Andraychak said.
As of 5:15 p.m., negotiators were at the scene attempting to get the suspect out of the building.
