Govt defends HECS debt rise

Education Minister Christopher Pyne is defending the doubling of student loan debt over the next four years.

The mid-year budget update released on Monday showed almost two million people owed $25.1 billion under the Higher Education Loan Program as of June 30.

By the end of this financial year the amount of loans would grow to $30.6 billion before heading to $52 billion in four years.

The federal opposition seized on the figures as proving students will pay more for their education and $100,000 degrees will become a reality under the government's plan to deregulate university fees.

But Mr Pyne's office told AAP on Tuesday the increase reflected a number of underlying growth pressures.

"It's not primarily attributable to increased student fees under the government's higher education reforms," a statement said.

A major driver was broadening access to student loans to the vocational education and training sector.

The growing HECS debt is a government asset and investment in Australia's skills base, the minister's office said.