The zoo says Mei Xiang gave birth at 10:46 p.m. Sunday. It says the staff can hear the cub, but has yet to see it because Mei Xiang has built a large nest in her den.
The cub is the second born to Mei Xiang and Tian Tian as the result of artificial insemination.
Mei Xiang has had five consecutive pseudopregnancies since 2007. She gave birth to her only other cub, Tai Shan, in 2005.