Jeremy Corbyn and Labour leadership rival Owen Smith were told they were both unelectable and should step aside for another candidate as the pair went head to head in a live television clash.
Audience members booed and jeered in the fractious opening minutes of BBC One's Question Time hustings.
The Labour leader has no support from his MPs and his challenger has no support from the party, they were told.
"The squabbles have made the party look unelectable and both of you look unelectable," an audience member said. "You should stand aside and let someone else, maybe Harriet Harman, somebody, just anybody lead the party to victory."
One voter told the candidates "I can't say my heart is beating for either side" while another said supporters of both were booing "but I've heard mostly from Jeremy's side" as she bemoaned the state of the party.
Mr Corbyn said he believed Labour would "come together" after the results of the leadership battle, which he is on course to win comfortably, are announced.
Mr Smith told the audience he was "incredibly confident" that he would be victorious on September 24.
Mr Corbyn said he had been talking to Labour MPs in recent weeks and believed they would turn their fire on the Conservatives after the contest.
He said: "I think after the election is over and after the conference is over you will see the wish of MPs to reflect the wishes of party members all over the country that there is a coming together in order to oppose this Tory government."
Mr Smith said Labour would be out of power for a generation if Mr Corbyn remains in post.
He said: "I say to everybody in the Labour movement right now, it's in your hands, the choice is with you as to whether we want to be with Jeremy and in opposition, potentially for a generation, or start leading the way back to Labour being in power."
Mr Corbyn's aides suggested on Wednesday that the leader might rule out full membership of the European single market unless Britain can negotiate exemptions from key EU rules.
The Labour leader said he wanted to remain in the single market "if it's possible and I think it probably is".
Mr Smith said he wants Labour to promise at the 2020 general election to take Britain back into the EU.
Asked if that means to ignore the Brexit vote, he replied: "Well, exactly."