Have a look here (of course an unofficial community build, I hope FriendlyARM will also offer something official when the 2GB variant of T3 comes out):
https://github.com/rafaello7/debian-installer-nanopi-m3/releases
https://github.com/rafaello7/debian-installer-nanopi-m3
https://github.com/rafaello7/linux-nanopi-m3
All credits for this effort go to github user "rafaello7" - I'm just the messenger...
Best regards,
awl