Looking ahead to next year's general election, Mr Cunliffe said Christchurch Central, which Labour lost in 2011 "will be a real battle and we have a few hurdles to cross for that one".
But the party had learned during the byelection campaign that "Christchurch people who've been affected by the earthquake, which is just about everybody, are heartily sick and tired of the slow rate of the rebuild and stressed and frustrated about the slow payout rates from the insurance industry.
"Some people are doing really well out of the rebuild but most aren't and there's a sense of unfairness that's come through, particularly in Christchurch East but more broadly as well.
"So I think there's definitely a seachange on in greater Christchurch in terms of the mood and I think Christchurch people increasingly want a fresh start next year. They've shown that in the mayoral election as well."
Through a spokeswoman, Prime Minister John Key said National didn't take any seats for granted, "and we're sure Christchurch Central will again be fiercely contested in 2014".
"However, we do not think the Christchurch East result makes winning Central any easier or more difficult."
Mr Cunliffe paid tribute to Ms Williams, saying she was "obviously a very good candidate who is a very genuine person" and who had demonstrated she cared for "a constituency that's been battered and bruised".