Hundreds farewell Robin Williams in San Francisco ceremony organised by daughter Zelda

Celebrity friends have joined hundreds of mourners farewelling Robin Williams in a special private ceremony today, six weeks after the comedian's death.

Billy Crystal and Whoopi Goldberg led the tributes at the Curran Theatre in San Francisco where family and friends gathered around Williams' wife, Susan Schneider, and children Zak, Zelda and Cody.

The majority of the memorial was planned by 25-year-old Zelda, according to sources.

US media reports there was a musical tribute by Stevie Wonder with the Glide Memorial choir and mourners included cyclist Lance Armstrong, director George Lucas and actor Danny DeVito.

Crystal "was in tears" as he opened the two-hour memorial, a source told US magazine.

The Hollywood Reporter said other attendees included Bette Midler, Ben Stiller, Sarah Michelle Gellar, Minnie Driver, and Josh Groban.

The tribute was followed by a reception at Westin St. Francis Hotel.

Williams took his own life on August 11, aged 63.

New York Daily News reports he was cremated and his family plans to scatter his ashes in San Francisco Bay.