Singer-songwriter Michelle Shocked has shocked fans after launching an anti-gay rant onstage in San Francisco on Sunday night. The singer – who became a favourite of leftwing music fans with early albums such as The Texas Campfire Tapes and Short Sharp Shocked, but who is now a born-again Christian – began telling the crowd her views of Proposition 8, California's legal definition of marriage being a union between a woman and a man.

"When they stop Prop 8 and force priests at gunpoint to marry gays, it will be the downfall of civilisation, and Jesus will come back," Shocked told the crowd at Yoshi's in San Francisco, before many of them reportedly walked out. "You are going to leave here and tell people, 'Michelle Shocked said God hates faggots.'"

The club's manager tried to end the show, but Shocked continued playing until venue staff pulled the plug and turned off the stage lights.

Shocked, 51, has been an alternative music icon since the late 80s and early 90s, when her raw sound and radical politics briefly caught the zeitgeist. Although she is from Texas, she was particularly successful in the UK, where three of her LPs reached the top 50. Though Shocked's popularity has waned, she has continued making music, describing herself as an "anarchist skateboard punk" and, for about two decades, a born-again Christian.

Audience members at Sunday's show were stunned by her remarks. "She said gay marriage would cause the end of the world," tweeted @anile02. "She's a total bigot and said so on stage," agreed @lisahubbert. "It was unreal. We had to leave." @TheGuapo said he felt like an "emotional hostage": "[she] went full hate speech".

Several venues – in Illinois, California, Oregon and Colorado – have now cancelled forthcoming shows.

Shocked has not directly responded to these developments, except to tweet: "Truth is leading to painful confrontation."

In a 2008 interview with the Dallas Voice, Shocked strongly denied rumours that she is a lesbian. "[But] what if we called you an 'honorary lesbian'?" asked the interviewer. "I would be honoured," she replied. Describing herself as a "devout practising Christian", she said she was still coming to terms with "bigotry" in the church. "According to my Bible, which I didn't write, homosexuality is immoral," she explained. "But homosexuality is no more less a sin than fornication. And I'm a fornicator with a capital F."