Tertiary enrolments have reached their lowest point in more than a decade amid rising costs and a lack of financial support, the Union of Students Associations says.

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Education Ministry figures show 353,000 domestic students - or 9.4 percent of the population aged 15 years and over - were enrolled in tertiary education last year.

That followed a steady decline from 423,030 people - or 12.5 percent of over-15s - in 2009.

The fall in participation occurred across all age groups except under-18s and was biggest among those over 40, where participation nearly halved from 6.7 percent to 3.6 percent.

Māori continued to have the highest rate of participation in tertiary education at 16.9 percent but down from 19.5 percent in 2009.

The president of the Union of Students' Associations, Jonathan Gee, said lack of financial support for students was behind the declining participation rate.

"The cost of living, that's a big issue at the moment in terms of rent costs - 40 percent of tertiary students live in Auckland, you imagine the high rent costs they have to pay. There is rising costs, yes there's always been student debt, but student support is failing to keep up with those rising costs," Mr Gee said.

He said older students were particularly hard hit because people over 40 were no longer eligible for student allowances and those over 55 could not get student loans.

"I'm getting calls all the time from mature students saying that they're worried about that cap or that they've taken some time off study and now they can't re-enrol and get the allowance because they're over 40," he said.

Mr Gee said even people who had started a tertiary course were dropping out because of the costs involved.

"They go into tertiary education they see the amount of debt that they've incurred over that year, they freak out, their families freak out, and they decide 'no, I'd rather be earning rather than learning'," he said.

The Education Ministry's deputy secretary graduate achievement, vocations and careers, Claire Douglas, said the decline in tertiary participation over the past decade was mainly in non-degree qualifications.

"Over the 10-year period this drop will in part reflect government efforts to lift quality in the tertiary sector," she said.

Ms Douglas said between 2015 and 2016 the proportion of students going from school to tertiary study dropped two percentage points, or 414 students.

But she said school-leavers' progression to bachelors-level study went up 0.8 percentage points from 2015 to 2016, while non-degree and certificate study fell 1.4 to 1.5 percentage points.

"Overall there has been a 4.1 percentage point increase in the proportion of school leavers going to bachelors study from 2011 to 2016," she said.

The executive director of Universities New Zealand, Chris Whelan, said universities had not been affected by the drop in participation or by the fall in the number of school leavers entering tertiary study.

In fact, universities enrolled 480 more 18 and 19-year-olds last year than they did in 2015.

However, Mr Whelan said university enrolments might be affected in future by increases in the number of students taking a gap year between finishing work and starting study, and by students choosing to study overseas.