One of New Zealand's oldest electorates will have a new MP after September 23.

But that's about all that is guaranteed in the race to be Whanganui's next representative in Parliament.

While the electorate remains Whanganui in name it now has much broader reach than ever with population decline over the years stretching the boundary deep into Taranaki.

Changes following the last election mean Midhirst, north of Stratford, came into the Whanganui electorate, while on the other side of Mt Taranaki it takes in Opunake.

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The fact is Whanganui now only occupies a small piece at the bottom of a vast electorate, geographically.

But the city still holds a majority of the area's population.

Whanganui is one of the oldest electorates in the country, formed in 1860 when the Wanganui-Rangitikei seat was split in two.

Since 1935 the seat has been held by Labour or National since the inception of the two parties.

Retiring MP Chester Borrows is the only National Party MP to hold it for more than one term.

It has been a stable seat with only Labour's Jill Pettis and Mr Borrows (four terms each) holding it since 1993.

But despite Labour's dominance over three quarters of a century Whanganui is no longer as red as it used to be.

The early signs are that Harete Hipango will hold it for National by a whisker.

Having said that, Labour and candidate Steph Lewis have targeted this seat since Mr Borrows stepped down and 2017 is Labour's best shot in years to wrest the seat back.

Labour's own polling and the New Zealand Herald election forecaster puts Ms Hipango's lead at just under 2 per cent.

That is far closer than in 2014 when Mr Borrows won a 4500 majority over now Whanganui mayor Hamish McDouall even though Mr McDouall had been closing the gap each election since 2008.

What's also changed this year is the two largest minor parties are back in the running after sitting out 2014.

The Greens have put up Horizons Regional Councillor Nicola Patrick and Reg Skipworth is running for New Zealand First, which arguably may do more to help Ms Hipango than Ms Lewis.

Alan Davidson for Act is the only candidate returning from 2014.

In terms of party vote, Whanganui has overwhelming voted for National in the past three elections, close to mirroring national trends.

Ideas for regional development is something voters will be looking for in candidates with major announcements from both National ($6 million for the velodrome roof) and Labour ($3 million to repair the north and south moles) already made.

The electorate is also the focus for one of the major environmental issues of the election.

The pending iron sand mining off the coast on Patea sits in right the middle of the electorate and has already been the subject of a policy announcement by the Greens to turn the area into a marine mammal sanctuary.

Almost half those employed in the electorate work in one of four industries: manufacturing (16.6%); agriculture, forestry, and fishing (13.2%); health care and social
assistance (10.8%); retail trade (9.2%).