Two newborn giant panda twin cubs rest in an incubator at Toronto Zoo in Toronto, Canada, Oct 13, 2015. Female giant panda Er Shun, who is on loan from China, gave birth to the twin cubs at 3:31 am and 3:44 am Tuesday. [Photo/Xinhua]

TORONTO - A giant panda at the Toronto Zoo gave birth to twin cubs on Tuesday, the first baby pandas born in Canada since the zoo accepted two pandas on loan from China in 2013.

Er Shun gave birth to the cubs 13 minutes apart shortly after 3 am ET, the zoo said in a statement. The cubs weighed 188 grams and 115 grams at birth and their sex has not yet been determined.

"Er Shun is demonstrating excellent maternal instincts and began cleaning and cradling the first cub soon after its birth," the zoo said in the statement.

"While this is wonderful news, the tiny cubs are very vulnerable at this size, so the next several hours and days will be critical to their survival."

The cubs, about the size of a guinea pig, were conceived through artificial insemination using sperm from her Toronto Zoo partner Da Mao as well as the frozen sperm from two giant pandas living in China. The paternity of the cubs may not be known for several months, the zoo said.

The cubs, born pink with sparse white hair, will be cared for in a maternity area of the giant panda house for several months, and "twin-swapped" between an incubator and their mother so they have time to bond with Er Shun.

Er Shun and Da Mao are on loan from China for 10 years as part of a long-term breeding program. They will remain at the Toronto zoo until 2018 and then relocate to the Calgary Zoo for five years.