Toronto Zoo giant panda newborn cubs, born to Er Shun on October 13, 2015. (TORONTO ZOO FOR CHINA DAILY)

It's a Canadian first: the birth of two giant panda cubs.

Er Shun gave birth to her first cub at 3:31 a.m. on Tuesday at the Toronto Zoo; the second cub was born at 3:44 a.m. The first born cub weighed 187.7 grams and the other one was 115 grams. Mother and babies all appear to be doing well, according to zoo officials.

Er Shun — who is on loan from China along with male panda named Da Mao — is showing “excellent maternal instincts” and has been given time to bond with each cub as they take turns in an incubator in the maternity area of the giant panda house, which is closed to the public, the zoo said.

Giant panda cubs are born blind and weigh only 0.08 to 0.2 kilograms, and are about the size of a stick of butter. They are pink in color, with short sparse white hair, and are 1/900th the size of their mother, one of the smallest newborn mammals relative to its mother’s size.

“The tiny cubs are very vulnerable at this size, so the next several hours and days will be critical to their survival,” the zoo said in a statement.

Toronto Zoo Head Veterinarian and giant panda experts from China attending to newborn twin cubs, October 13, 2015 at the Toronto Zoo. (TORONTO ZOO FOR CHINA DAILY)

Er Shun underwent two non-surgical artificial insemination procedures in May using sperm from male panda Da Mao and frozen sperm collected from two other giant pandas in China. The zoo announced she was pregnant on Sept 30. The zoo staff doesn't yet know the sex of the cubs and has not confirmed which panda is the father, and it may be several months before that can be determined.

The Toronto Zoo is working with panda experts from the Chengdu Research Base of Giant Panda Breeding in China. Er Shun and Da Mao are on loan to the Toronto Zoo from China, as part of a long-term conservation and breeding program.

The giant pandas will remain in Toronto until 2018, and then will relocate to the Calgary Zoo in Alberta. Zoo staff have said the cubs, if they survive, will live at the zoo for about two years and will likely return to China once they are weaned from Er Shun.

“We are so proud to be contributing to the ongoing survival of this endangered species,'' said John Tracogna, CEO of the zoo.

Councillor Raymond Cho, chairman of the Toronto Zoo Board of Management, said, "We look forward to sharing our learnings with scientists around the world in the hope this will help us save this endangered species."

renali@chinadailyusa.com