Australian political parties have cut loose or chastised several of their own candidates for sexist, anti-Muslim, racist and homophobic behavior less than three weeks before elections, with most falling victim to their own online histories.

The scandals surrounding candidates have become recurring distractions for Prime Minister Scott Morrison and opposition leader Bill Shorten this week as they attempt to sell their policies on the campaign trail.

Morrison on Thursday stood by Liberal candidate Jessica Whelan against accusations that she made anti-Muslim posts on social media.

Morrison says Whelan's social media comments appeared to have been doctored and a complaint had been made to police.

Parties cannot replace dumped candidates because the ballot papers have already been printed and early voting began on Monday.