The sister of former prime minister Tony Abbott said protesters "shredded" her outfit and tried to punch her in "ugly" scenes outside a Liberal Party fundraising dinner in Sydney on Friday evening.

Christine Forster said she was pushed and shoved by Manus Island protesters as she and her partner, Virginia Edwards, tried to make their way to the event at the Australian Technology Park at Eveleigh, near Redfern.

"Essentially people surrounded us, they were spitting, they were snarling," Ms Forster said.

"It was extraordinary, it was a riot with people screaming in our faces, trying to spit at us, trying to punch us."