Possible low turnout on Saturday could favour 'underdog' National in Mt Roskill by-election

Prime Minister John Key and Mt Roskill by-election hopeful Parmjeet Parmar visit the Waikowhai Intermediate School in Mt Roskill. Photo / NZME

A probable low turnout in the Mt Roskill by-election could favour National and get its "massive underdog" over the line, Prime Minister John Key has suggested.

The Auckland electorate on Saturday will decide who will replace its long-serving MP Phil Goff, who resigned from Parliament to become Auckland Mayor.

The low profile of Labour's candidate and local board member Michael Wood and National backbencher Parmjeet Parmar, combined with the Kaikoura earthquakes, has meant the by-election hasn't generated many headlines.

Speaking this morning, Key said the turnout would likely be low.

"And we win the party vote there. So, in theory, if we could get our people to turn out and Labour's people didn't turn out as much, we could get there," he told Radio New Zealand.

National has been happy to highlight its underdog status since the by-election was announced, and Key continued that line this morning.

"You'd have to say we are the massive underdog solely because no incumbent government has won a seat they don't hold [in a by-election]."

In emails to supporters, Labour has stressed how much is at stake if Parmar does upset its candidate.

"If we lose this seat, National and Act will have an outright majority in Parliament, meaning they can pass any law they choose. That's why it's so important that we keep Mt Roskill red," Labour's general secretary Andrew Kirton wrote in the email.

After New Zealand First leader Winston Peters' Northland by-election victory in 2015, the number of National MPs dropped to 59, meaning it relied more on the Maori Party or United Future to get a majority to pass certain legislation.

Most notably, the Government was forced to go back to the drawing board on planned changes to the Resource Management Act, intended to speed up planning and consent laws. After lengthy negotiations, Environment Minister Nick Smith this month announced that the Maori Party will support the Resource Legislation Amendment Bill.

In his email, Kirton also called for supporters to donate to help the Mt Roskill by-election campaign.

Hoardings for Parmar outnumber her rival's on some of the main routes in Mt Roskill, which includes the Auckland suburbs of Lynfield, Wesley, Hillsborough and parts of Three Kings and Sandringham.

Her team say they have "well over" 250 up across the electorate, while Wood's have 170 large hoardings and 100 small.

Wood's campaign manager Shayne Misselbrook said hoardings were a "particularly ineffective" way of campaigning, and Labour had spent on other areas such as individually addressing enveloped mail for letterbox deliveries.

Wood will this week be at school gates at 3pm each day, conduct street corner meetings and door-knock most afternoons. Labour leader Andrew Little will join him for a full day of campaigning on Friday.

In the 2014 general election Goff won with an 8000-vote majority over Parmar but National got 14,275 party votes - about 2000 more than Labour.

National will be hoping Goff's departure will see enough people who split their vote in 2014 give Parmar their support this time.

Traditionally a Labour stronghold, gentrification and rising house prices are changing the make-up of some areas within Mt Roskill. However, the fact that Mt Roskill Grammar School's decile ranking was unchanged at 4 when recalculated in 2015 shows the limitations of that change.