Labour is worried about holding Mt Roskill in next month's by-election and National has a chance for a rare win, Prime Minister John Key says.
National's candidate Parmjeet Parmar kicked off her campaign on Saturday with Mr Key. They visited business in the electorate and spoke to a crowd of party faithful.
"We think there is a chance here. No incumbent Government has won a seat they don't hold so we're quite realistic but there's a sort of one in 20 year chance to get a National MP as MP for Mt Roskill," Mr Key says.
He says Labour isn't doing very well with ethnic communities, which are represented in the electorate.
"They [Labour] are worried about Mt Roskill and they should be worried," he says.
National launched its bid for Mt Roskill just hours before Labour made an official campaign visit to the electorate as part of their annual party conference.
Still, he says if National don't win Mt Roskill it won't mean anything for the general election in 2017.
Dr Parmar, a current National list MP, who is based in Mt Roskill, says she's been working hard on local issues and wants them to be the focus of the campaign.
She says Labour has taken the seat for granted.
"As a mother, a scientist, a businesswoman, and a dedicated community advocate, I am the only candidate with the local track record of experience and success in getting things done on Mt Roskill's behalf."
The Mt Roskill by-election is being held on December 3.
Michael Wood is standing for Labour. The newly formed People's Party will stand Rohan Nauhria while Auckland lawyer Adam Holland is set to run as an independent after missing out in the Auckland Council elections.
The by-election is necessary after incumbent Phil Goff was elected as Auckland mayor last month.