Melbourne Zoo's prized Asian elephant, Num-Oi, is now a mum after giving birth to a male calf.

The elephant's first-born arrived at 2.50am (AEDT) on Thursday following a 22-month pregnancy and a lengthy labour, with fellow mum Kulab and her two-year-year-old calf Ongard standing by, Melbourne Zoo said in a statement.

While the newborn is the first calf for Num-Oi, he's the fourth from the zoo's fertile bull elephant, Bong Su.

It's just the third elephant calf ever to be born at Melbourne Zoo.