The rhinoceros stillborn at Hamilton Zoo on Friday had a ruptured liver.
A post-mortem examination has found the calf died of internal bleeding.
The calf was born to the zoo's Southern White Rhino, Kito.
The zoo said the birth process was not prolonged, and the cause of death is a rare but recognised condition seen occasionally in larger mammals.
Zoo curator Samantha Kudeweh said staff were in shock and were upset about the loss.
It was the second time Kino had given birth, after the birth of a male calf in 2010, who was initially born blind.
- Newstalk ZB and nzherald.co.nz