The biggest museum fundraising campaign in San Francisco history is nearing its $610 million goal two years before the opening of a new wing that will more than double the space for artworks by Andy Warhol, Mark Rothko and David Hockney.

About $570 million, or 94 percent, has been raised by the San Francisco Museum of Modern Art for its 235,000-square-foot (21,800-square-meter) expansion and to add $245 million to the museum’s endowment. The $305 million wing designed by the Snohetta architecture firm is rising behind SFMOMA’s current home, opened two decades ago in the technology-heavy South of Market area, or SOMA.