You need an ETA for Northern Mariana Islands if you have an Australian passport

Travellers need a travel authorization to visit Northern Mariana Islands for Business or Tourism. The Guam and the Commonwealth of the Northern Mariana Islands Electronic Travel Authorization (G-CNMI ETA) is an online application that determines the eligibility of visitors to enter Northern Mariana Islands. Once the application is approved, travellers receive their G-CNMI ETA confirmation electronically. A valid International Civil Aviation Organization (ICAO) compliant, machine-readable passport is required. A valid G-CNMI ETA is required to visit the country. If the G-CNMI ETA is expired or doesn’t match the traveller’s passport information, travellers will not be able to board their flight. A G-CNMI ETA is electronically linked to a passport and valid for 2 years. If travellers receive a new passport, they must apply for a new G-CNMI ETA. Northern Mariana Islands permanent residents or holders of valid Northern Mariana Islandsvisas don’t need a G-CNMI ETA.