The by-election in Mt Albert will be held on June 13.

The seat is being vacated by former prime minister Helen Clark, who has been appointed head of the UN Development Agency.

Prime Minister John Key says the last day for nominations, in what is considered a safe Labour seat, will be May 19.

Three National candidates have been nominated with the party believing it is in with an outside chance, considering the party vote in Mt Albert separated Labour and National by just 2,500 votes at the election.

List MP, and this country's first Korean MP Melissa Lee, is expected to get the nod.

Nominations for Labour close on Wednesday.