The trend looks set to continue. Statistics NZ projects that 30 per cent of all pensioners will be working by the mid-2020s.
Malcolm Menzies, research manager for the Commission for Financial Literacy and Retirement Income, said the trend was mostly driven by universal superannuation, which is paid to all people over 65, regardless of their employment or financial status.
He said there were many reasons to stay in work.
"Some people need to stay on because they want to use those extra few years to build up their retirement savings. We think that some people have lost ground through the finance company crashes, and they're trying to make it up again. And some people just like their jobs.
"People who divorce in the last 10 years before retirement have significantly worse financial outcomes - that might be another reason why people carry on working."
Mr Menzies said many working pensioners simply stayed in the same job because employers could be reluctant to take on older workers.
Those who did find new jobs tended to get part-time work.
Grey Power national president Roy Reid said the rising cost of living was behind the trend.
"The costs of rates, electricity and food keep increasing. Superannuation is not keeping up with it, and for people to maintain their lifestyle, they have to find additional income."
Mr Reid said not all workers over 65 were doing it because they had to.
"Some of them enjoy even part-time work because it helps keep them fit and healthy and alive. But on the other hand, there are lot of people who, because of heavy manual work all their lives, are incapable of work."
Alpha Recruitment managing director Colin Mathieson said about half his over-65 temping clients were working because they had to.
He said older workers were reliable, experienced and had good life skills but took longer to adjust to new technology and needed more training.
Job keeps driver's wheels moving
At 75, Allen Davies is still working because he gets a kick out of it - but also because he would struggle without the income.
The electrical engineer has worked as an electrician and an electrical inspector, but now he's most comfortable behind the seat of the bus he drives on Waiheke Island.
"I meet people, I talk to people, so I enjoy that. But it also provides me with that income.
"What I'm doing, I quite enjoy doing - but also if I didn't have that income I think I'd go under, to be perfectly honest."
Mr Davies said his lifestyle would change "quite dramatically" if he went down to living just on super.
He said his 88-year-old sister no longer worked, but she had to dip into her savings every month to help cover her rates, power and other costs.
Senior service
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• Sam Neill, Hollywood actor, 65