A giant panda at Toronto Zoo has given birth to two cubs - the first ever to be born in Canada.
"We're really, really excited," zoo spokesperson Jennifer Tracey told INSIDE EDITION. She said the new additions are doing well.
"So far, so good," she said. "It's early days so they are very vulnerable. The next few days will be really vital."
The first cub weighed 187.7 grams when it was born, while the second weighed just 115 grams. Staff do not yet know their genders. Giant panda cubs are born blind and are about the size of a stick of butter, the zoo said.
Er Shun underwent two artificial insemination procedures in May involving sperm from different giant pandas. Officials do not yet know who fathered the cubs.
Staff said Er Shun has already demonstrated great maternal instincts and began cleaning and holding her first cub soon after its birth.
Following the second birth, zoo staff put the cub in an incubator in the maternity area of the panda house. Two hours later, the cub was swapped for the other twin so it could start bonding with their mom.
The cubs will stay in the maternity area of the giant panda house for several months and will not be visible to the public during that time.
In a statement, Toronto Zoo's Chief Executive Officer John Tracogna said: "We are so proud to be contributing to the ongoing survival of this endangered species. The Toronto Zoo has been a leader through its unique and successful reproductive programs and these historical births are a testament to the commitment and passion of the professional staff who work tirelessly every day to ensure the ongoing survival of so many species."
The giant pandas are on loan to the zoo as part of a long-term conservation breeding program. They will relocate to the Calgary Zoo in 2018.