Auditor-general Brendan Worrall has warned long-term financial sustainability is a major and increasing risk for many Queensland councils as the sector deals with a $5.4 billion debt.

After examining the books of 76 of Queensland's 77 councils for 2017 and 2018, the Queensland Audit Office report that was tabled in parliament on Wednesday warned the five-year average operating surplus ratio continued to deteriorate as the sector was still spending more than it earned.

The report also added “breaking even or making a small surplus over the long term is important for financial sustainability” and came after a similar warning last year.