Labour leader Jacinda Ardern says former leader Andrew Little asked her to take over six days before he resigned, the Stuff news agency has reported.

The agency says Ardern was questioned by a local at the Blackball "Formerly Hilton Hotel" on the West Coast yesterday about why she ended up in the job.

She said Little approached her on July 26 - her birthday - saying he didn't think he could turn things around for the party and she should take over as leader.

She refused and told him to "stick it out", the agency reported.

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Labour had already started falling in the polls on July 26, dropping in TVNZ's Colmar Brunton poll from 30 per cent on June 7 to 27 per cent on July 10, and was about to learn that it was down to a record low of 24 per cent in a poll taken on July 22-27 and published on July 30.

Internal Labour Party polling was likely to have been telling the same story when Little approached Ardern. The party's pollsters UMR put Labour on 23 per cent in late July.

Labour rebounded dramatically after Ardern took over as leader, jumping to 43 per cent in the Colmar Brunton poll by late August and overtaking National for the first time in more than a decade.