The ratings agency report, released on August 26, show outstanding payments in the 4825 post code have risen to a rate of 2.1 per cent.

Mount Isa is joined by three other Queensland post codes struggling to make repayments, with Laidley in the Lockyer Valley, and Brisbane suburbs Petrie and Kingston all in the nation’s top five.

The news isn’t all grim for the sunshine state though.

Queensland has been replaced this year by Tasmania as the worst performing state in Australia for mortgage repayments.

The average rate of delinquent mortgages in Tasmania is 1.33 per cent.

“This figure reflects Tasmania's high unemployment rate and low house appreciation over the past three years,” the report said.

Fitch said these two factors – local unemployment and housing markets – were driving regional mortgage performance, given the low interest rates Australians are seeing.

With this in mind, the report said metropolitan areas bore the brunt of the pain, with the exception of regions such as Mount Isa, who are coping a downturn in mining.

"The slowdown and job cuts in the mining industry have hit non-metropolitan regions in the outback of Western Australia, in Northern Territory, and in the north and outback of Queensland," the report said.

Fitch director James Zanesi told The North West Star it was “surprising” to see regions reliant on high-income industries, such as mining, top the list for mortgage delinquencies.

Mr Zanesi said it was usually “postcodes with low incomes” such as Ipswich or Logan, south of Brisbane, whose borrowers strained to pay back home loans.

Mount Isa has not cracked the top 20 postcodes for mortgage delinquency in the past five years, Mr Zanesi said.

Mackay, in Queensland’s central-east, is another example of a region heavily reliant on mining where homeowners are feeling the loan repayment grief.  

The coal mining region became the worst-performing post code in Australia this year for the first time, Fitch reported.

It followed a 59 base point worsening in 30 days or more arrears.

Queensland’s best-performing region by value is Inner Brisbane.

Top 10 postcodes for mortgage delinquency: 

1. 4502 Petrie, Qld (2.4 p pc)

2. 4341 Laidley, Qld (2.3 pc)

3. 3214 Corio, Vic (2.3 pc)

4. 4825 Mount Isa, Qld (2.1 pc)

5. 4114 Kingston, Qld (2.0 pc)

6. 2262 Budgewoi, NSW (2.0 pc)

7. 5108 Salisbury, SA (2.0 pc)

8. 3337 Melton, Vic (1.9 pc)

9. 3976 Hampton Park, Vic (1.9 pc)

10. 6066 Ballajura, WA (1.9 pc)