San Francisco braced on Friday for a weekend of protests, including a rally by an Oregon-based group that local leaders labeled "white supremacist" as the city's mayor urged residents to boycott the event, Reuters has reported.

The demonstrations planned for Friday, Saturday and Sunday across the Bay Area raised concern among San Francisco police and elected officials two weeks after right-wing activists, including neo-Nazis and the Ku Klux Klan, fought with anti-racism protesters in the streets of Charlottesville, Virginia.

A woman was killed at that "Unite the Right" rally when a man thought to have neo-Nazi sympathies drove his car into a crowd of counter-protesters. Nineteen other people were injured.

The Saturday event is billed as a "free speech" rally, but critics say the Oregon-based organisers, Patriot Prayer, is a white nationalist group, pointing to plans that may include the far-right Oath Keepers to provide armed security. The group has decried racism and neo-Nazis.

Last weekend, 33 people were arrested in Boston as tens of thousands of demonstrators took to the streets to protest a "free speech" rally featuring far-right speakers.

In San Francisco, city officials including Mayor Ed Lee had lobbied the National Park Service to deny a permit for Patriot Prayer to hold a free-speech event at Crissy Field, which is under federal control as part of the Golden Gate National Recreation Area.

When that permit was granted on Wednesday, Lee told residents of San Francisco to essentially boycott the rally.

"I ask our public and our residents of the San Francisco Bay Area to honor our request to not dignify people who are coming in here under the guise of patriot and prayer words to really preach violence and hatred," Lee told a press conference.

The mayor urged locals to instead attend city-hosted events on Friday and Saturday that he said would focus on "inclusion, compassion and love rather than hate," Reuters added.