The two giant panda cubs born at the Toronto Zoo just weeks ago have tripled in size, zookeepers say.

The cubs have developed more white fuzz over their bodies, while their black markings and thicker fur is also starting to come in. And the cubs are developing thumb pads on their paws which will help them hold bamboo when they are older.

The smaller panda of the two is now 20 centimetres long and weighs 422 grams. The larger cub is 23 centimetres and weighs 672 grams.

Er Shun is one of two pandas on loan to the zoo from China. Along with the cubs, she has been under constant observation by experts from Chengdu Research Base of Giant Panda Breeding in China since their birth.

The zoo says she continues to be a great mother to the cubs.