Several blocks in the Bernal Heights neighborhood of San Francisco are shut to traffic as police carry out an investigation on Friday.
Police told KTVU the crisis negotiations team is interacting with a man "who may be experiencing a mental health emergency" and was armed.
The incident began unfolding at Powhatten Avenue and Bradford Street at 10:45 a.m., police said.
The public is asked to avoid the area. Drivers can expect delays in the neighborhood.