The success of Labour-aligned candidates in Auckland, Wellington and Christchurch mayoral contests will give party members a boost, Labour leader Andrew Little says.
However, Little isn't reading too much into the local government results ahead of next year's general election - saying that contest is a "different beast".
"It's a little too early to say whether there is a change in mood. But certainly the mayoral results in Auckland, Wellington and Christchurch are good," Little told the Herald before heading to new Wellington mayor Justin Lester's victory party.
"They will give people a boost, and that's a good thing."
Labour MP Phil Goff easily won the Auckland mayoral contest, and former Labour MP and incumbent Christchurch mayor Lianne Dalziel beat nearest rival John Minto by 60,000 votes.
Little said those results underlined the importance of well organised, ground-level campaigning.
"But, beyond that, I wouldn't read too much into it. We have our own work to do, and that's what we will be focused on next year ... I wouldn't read too much into [the results] in terms of a general election - it tends to be a different beast."
Following his election as Auckland Mayor, Goff will resign from Parliament next week. That will allow for a byelection in Mt Roskill before Christmas.
National Party president Peter Goodfellow said his party would select a candidate on October 19, with nominations opening next week.
Mt Roskill-based list MP Parmjeet Parmar is all but assured of selection.
Capturing Mt Roskill will be "very difficult", Goodfellow said, as no government had ever won a byelection off the Opposition.
"And of course, Labour and the Greens have done a deal for the seat to try and make it even less likely.
"We will however run a strong campaign. Labour has held Mt Roskill since it was created in 1999 and tends to take the electorate a bit for granted."
The Green Party last week announced it would not stand a candidate in the byelection, with co-leader Metiria Turei saying it would be closely contested and the Greens didn't want to "play any role in National winning the seat".
That deal is the first in an electorate under the agreement between Labour and the Greens to campaign together more closely and work to increase the centre-left vote.
It could prove critical - in 2014 Goff won with an 8000-vote majority over National's candidate Parmjeet Parmar but National got 14,275 party votes - about 2000 more than Labour.
Little rejected Goodfellow's criticism.
"We don't take [the electorate] for granted at all, that's why we have worked pretty hard to get a campaign team in place even before it was guaranteed there was going to be a byelection ... we have fundraising underway.
"If Peter Goodfellow has said that then he is more stupid than I gave him credit for."