UPDATED 4.52PM: National's Steven Joyce has accused Labour of panicking and 'pork barrel' politics for its Mt Roskill byelection pledge to put $680 million into a light rail system for Auckland.

In an announcement linked to the Mt Roskill byelection on December 3, Labour leader Andrew Little released part of Labour's transport policy for Auckland - $680m to help pay for the first stage of a light rail system from Wynyard Quarter to Mt Roskill.

Little, joined by Labour's byelection candidate Michael Wood, set out Labour's plan on Sunday for the Government to pay half of the $1.36b cost for light rail and Auckland Council the other half.

Joyce said the promise was "taking pork barrel politics to a whole new level."

"Labour are hitting the panic button fairly early on," Mr Joyce says. "Promising a $1.4 billion rail link between the electorate and the city looks very desperate."

"If this is the sticker price for a Labour party by-election campaign, all the other electorates across New Zealand will be asking for their $1.4 billion. To say nothing of every other electorate in Auckland looking for multi-billions in new railway lines.  And we've still got more than a month to go."

It has echoes of last year's Northland byelection, when National was accused of 'pork barrel' politics after Transport Minister Simon Bridges and its candidate Mark Osborne announced a promise to upgrade 10 one-way bridges in the region.

Joyce had overseen that campaign in which NZ First leader Winston Peters took the seat the National Party had long held.

Little said Auckland Council wanted to build light rail from Mt Roskill to the CBD within 10 years but the Government had refused to commit funding. 

The council has no money for light rail, but new mayor and former Mt Roskill MP Phil Goff has promised to bring forward light rail subject to a business case in the next long-term budget in 2018.

The 13km line would run via Britomart, along Queen St to Dominion Rd, ending near the Stoddard Rd-Sandringham Rd intersection, said Little, who was joined by Labour's candidate in the byelection, Michael Wood, at Dominion Rd in Balmoral.

Little said it was clearly needed to tackle congestion problems.

"Right now, gridlock is choking Auckland's ability to grow. Auckland is crying out for infrastructure projects to get the city moving, but the Government is out of touch and ignoring the problem. Labour will deliver, starting with a modern light rail line," Little said.

Little said the project would cut travel times, reduce congestion and pollution, improve health, and boost productivity. He said the homes of 29,000 people and 48,000 jobs are located within 500m of the planned stops, with major growth likely in the coming decade.

National's byelection candidate Parmjeet Parmar said Michael Wood's backing for the proposal was a change of tune, saying he had previously criticised it because it would delay upgrades to Dominion Rd.

"Just last year, my opponent issued a press release calling light rail 'not a fully formed proposal' and protesting that 'we don't have clear information about funding'.

Suddenly this year, after Phil Goff announced his support of light rail in his Mayoral campaign, Mr Wood was tweeting in support of it." 

Her own campaign would focus on local issues such as getting more buses, filling the gaps in bus routes, better bus shelters, changing T3 lanes and improving safety of footpaths.​

Little's view is it's an innovative infrastructure Auckland needs to get the city moving.

With additional reporting from Newstalk ZB's Felix Marwick.

-NZ Herald