An investigation by the Australian Skills Quality Authority (ASQA) has found problems with two-thirds of private training providers it audited.

A report released today by the government watchdog also revealed vocational education training cost the state and territories $5.9 billion in 2014-15.

That included $1.8 billion of Commonwealth money which was partly to fund VET FEE HELP - the controversial HECS-style student loan for private diplomas.

ASQA launched its investigation into 21 private companies after a big rise in student complaints about VET FEE HELP.

The investigation included private training giants Evocca College and Careers Australia, both of which have reaped hundreds of millions of dollars in federal funding.

The ABC has recently reported on complaints about both companies.

From 21 companies investigated, seven were fully compliant and eight had problems that required new conditions to be added. One company, Unique International College Pty Ltd, had its registration cancelled, and five are still under investigation.

They are Holmesglen Institute, Cornerstone Investment Aust Pty Ltd (Australian Institute of Commerce and Language, Empower Institute), Study Group Australia Pty Ltd (ACPE Academy, Martin College, Australian Institute of Applied Sciences, Embassy English), College of Creative Design and Arts Pty Ltd (College of Creative Design and Arts, Keystone College), Australian Institute of Professional Education Pty Ltd (Aipe, Australian Institute of Professional Education, Studyonline, Study Connect).

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Evocca College and Careers Australia were part of the group of eight companies that were allowed to continue to operate with added conditions.

Regarding Evocca, the ASQA report found, "non-compliance with the Standards regarding the RTO's assessment system, the accuracy of its marketing, and its complaint and appeals policies and procedures".

Careers Australia had made recent changes that made it compliant, the report found, but "ASQA considers it necessary to monitor the implementation of these changes".

ASQA said it would continue to watch how both Evocca and Careers Australia abide by their new conditions.

Craig White, the chief executive officer of Evocca, said in a statement the college was pleased to be advised of its continuing compliance following the audit.

"We look forward to continuing to provide ASQA with any information that it may request," he said.

"As an industry leader we fully support the various legislation and initiatives that have been and will be put in place that will assist in ensuring a quality regulated industry for students."

Careers Australia has so far declined to comment.