The Victoria’s Secret model – whose due date was in the first weeks of January - is said to have started having contractions in the early hours of this morning.
Orlando and her parents, Therese and John, are believed to be with her. The news comes after a false alarm on Boxing Day.
A family member told Australia’s Herald Sun newspaper: “We did get a text on Boxing Day saying she had gone into labour but it was false alarm but I can confirm she did go into labour early this morning.”
Miranda, 27, married Orlando, 33, in July and announced the pregnancy in August.
She found out she was pregnant while shooting a fashion campaign in Paris, France, following weeks of nausea.
Miranda’s parents flew from her home country at the end of December to be with her for the arrival of their grandchild.
The couple have previously stated they didn’t want to find out the sex of the child before the birth and the catwalk beauty has insisted she wants to completely focus on motherhood after the birth.
She said: "For me, family is life. The decision to start one wasn't complex at all.
"My career has been wonderful, but it's not my life. I don't feel pressure to get back to work."
Explaining her vision for the future, she added: "My goal involves a hammock, a vegetable patch, and a solar-powered house. And I hope to eventually get there."