These are based on Office for National Statistics population projections and life expectancy estimates.
Pensions Minister Steve Webb said the "staggering" figures brought home the need for pension reforms.
"Many millions of us will be spending around a third of our lives or more in retirement in the future," he said, adding that the government was determined to reform the pensions system to make it "sustainable for the long term".
The DWP estimates there will be at least 507,000 people aged 100 or over by 2066, including 7,700 people aged 110 or over - so-called super-centenarians.
Currently 11,800 people in the UK are aged 100 or over and fewer than 100 are over 110.
The government figures suggest that of the more than 10m who will go on to reach 100, 3m are currently aged under 16, 5.5m are aged between 16 and 50, and 1.3m are aged between 51 and 65.
About 875,000 are already aged over 65, it says.
The fear is that longer life spans will put an intolerable pressure on the pensions system and the NHS.
Dr Ros Altman, director general of the Saga Group, said pensions were not the only aspect of older life that needed to considered.
"Saving more and having a good pension is one thing - but there are also opportunities, and should be, for us to keep working longer, but not necessarily full time," she said.
"There is, in my view, a whole new phase of life which has been out there for grabs which still is available to us where we're not working full time. You're not suddenly stopping when you're in your 60s just because you've reached a particular chronological age.
"But you're thinking 'OK, what's my next career going to be?' - which is going to be part-time, let's say three days a week, four or five days a week off. But still earning some money, because at the end of the day, the state pension is not going to give you a decent lifestyle."