Labour says the Christchurch earthquakes pushed some of its voters out of the city, while National says its strong showing is a vote of confidence in the Government's leadership during the recovery.
Christchurch Central, a traditional stronghold for the Labour, hangs in the balance.
Incumbent Labour MP Brendon Burns and National's Nicky Wagner each won 10,493 votes, before special votes are counted.
Mr Burns says many of the residents who left the city after the earthquakes were from suburbs hit hard by the quakes such as Avonside, Richmond and Shirley, which are Labour heartland areas.
He expects those residents' votes to come through in the special votes which will not be announced until 10 December.
Ms Wagner says voters responded to the National government's earthquake recovery, and were put off by Labour's scare tactics.
She says she is is confident the special votes will swing her way given voter confidence in National's earthquake recovery leadership.
In Waimakariri, National's Kate Wilkinson took the seat by a mere 395 votes from the Labour Party's Clayton Cosgrove - who had previously held the seat by 390 votes.
Labour's Lianne Dalziel held Christchurch East, and the sitting Labour MP Ruth Dyson retained Port Hills.
For preliminary results in all seats go to Radio New Zealand's Electorates page.
