Inland Revenue said nearly 80,000 of the 111,000 New Zealanders living overseas were behind on their student loan repayments.
IRD collections manager Stuart Duff said about 22 percent of borrowers living overseas were in Australia.
He said the $840m owed to New Zealand was a substantial amount of debt.
"We're looking to make sure they can get in contact with with us and make some sort of arrangement to pay back their loan."
Around 22,000 New Zealand-based borrowers were in default, collectively owing about $79m on their student loans.