Australia AM Radio Bandwidth (courtesy of ACMA)
Melbourne stations: Here are some examples..

ABC Radio

Emission Center Frequency 774 kHz
Bandwidth 18 kHz
Emission Designator 18K0A3E
Transmitter Power 50000 W pZ

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Commercial Radio

Emission Center Frequency 1.278 MHz
Bandwidth 18 kHz
Emission Designator 18K0A3E
Transmitter Power 5000 W pZ

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Community Radio

Emission Center Frequency 855 kHz
Bandwidth 18 kHz
Emission Designator 18K0A3E
Transmitter Power 3500 W pZ

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Narrowband Area Service Broadcast Radio

Emission Center Frequency 1.692 MHz
Bandwidth 6 kHz
Emission Designator 6K00A3E
Transmitter Power 400 W pZ

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AM Band Spectrum Allocations

https://web.acma.gov.au/rrl/assignment_range.search?pSEARCH_LOCATION=139145%205%20Dunoon%20Street%20MURRUMBEENA%20VIC%203163&pSELECTED_LOCATION=139145%205%20Dunoon%20Street%20MURRUMBEENA%20VIC%203163&pSELECTED_LONGITUDE=145.0670043438889&pSELECTED_LATITUDE=-37.8912538325&pSELECTED_TYPE=SITE&pDISTANCE=150&pDISTANCE_UNITS=km&pLINKED_PATHS=&pLOW_FREQ=529&pHIGH_FREQ=1710&pLOW_FREQ_MULT=KHz&pHIGH_FREQ_MULT=KHz&pLOW_AUTH_DATE=&pHIGH_AUTH_DATE=&SUBMIT=distance&pSORT_BY=frequency&pSORT_DIR=asc

So as you can see, the bandwidth permitted depends on what category the station is
i.e. Government ABC/SBS, Commercial, Community or Narrowband.