National claimed a larger share of the party vote at the last general election, which came a year after the first big tremor.
Labour's Wigram MP Megan Woods said elections typically favoured the incumbent after a catastrophe such as the quake.
"The 2011 election followed the pattern we see internationally after a disaster. By and large you saw that with the electoral seats as well. Even though the party vote was lost, the results favoured their incumbent MP.
"The difference this time is three years of inaction. A lot of people that voted National last time have had a harrowing three years battling their insurance company, battling EQC."
Labour believes Christchurch Central in particular is a winnable seat. National's Nicky Wagner scraped to victory with fewer than 50 votes in 2011.
"Labour's taking Christchurch really seriously," said Christchurch Central candidate Tony Milne.
"We know there's a lot of anger and frustration in the city."
At the second Leaders Debate in Christchurch on Tuesday, Mr Key was grilled by residents on insurance companies' delaying tactics and Government's half-price compensation for red-zoned, bare land, which could not be insured. One resident said insurance companies were treating Cantabrians "with contempt".
Mr Key said Government had been as fair as possible, and repeatedly emphasized that the number of unsettled claims was "very small".
The Insurance Council released figures today which appeared to back Mr Key's claim. The data showed 90 per cent of private residential claims had been settled, and the remainder should be completed by 2016. Commercial property claims will take a little longer.
But Labour says four years, let alone six years, is far too long for homeowners to wait. It is promising to set up a specialised earthquake court to fast-track compensation, and will spend $20 million paying owners of bare properties the full value of their land.
National has pointed to progress in the central city as evidence of a rebuild that is gathering pace.
Mr Key told a group of Christchurch businesspeople on Tuesday that the CBD was moving from "demolition to construction".
Residents this week were divided about whether that was the case, with some pointing to the prevalence of empty lots and gaps in the cityscape.
Christchurch East MP Poto Williams said her electorate's problems were more acute than the CBD.
"Out East, we've got people who struggled before the quakes. And the quakes have really impacted on them quite badly."
Labour's first priority for the region would be rapidly increasing housing.
But if it is elected, its promise of 10,000 homes for Christchurch is unlikely to ramp up until the third or fourth year.
Ms Williams said Labour would bridge this gap by setting up 400 emergency houses within six months.
