Kim Kardashian West "can't believe" her daughter is four.

North and Kim Kardashian West

North and Kim Kardashian West

The 36-year-old reality TV star took to her official website and app to wish her "mini me" daughter North a happy birthday on Thursday (15.06.17) and admitted she is amazed at how quickly time flies.

She wrote: "Happy birthday to my mini me!

"I can't believe you are 4 already. I love you so much, Northie!"

Kim - who also has son Saint, 18 months, with husband Kanye West - also posted a video montage of herself and North, which included a number of old clips.

In one, the 'Keeping Up with the Kardashians' star told her daugher: "Are you not going to get any bigger? You're not going to get any taller. I want you to stay little forever, OK?"

In another clip, North told her mother: "I love you so much."

Kim replied: "Well, even when you're big, you're gonna be so nice to me?"

North said: "Yeah."

The clip also featured a number of Kimojis based on the little girl.

And North's famous grandma, Kris Jenner, shared a photo collage of her granddaughter on Instagram and admitted she felt "blessed" to see the youngster grow up.

She wrote: "Happy birthday to our beautiful, funny, smart little love bug, North.

"You bring so much light to our lives and I am blessed beyond words to have you as my granddaughter. It brings me so much joy to watch you grow up to be sweet and kind and loving... I love you so much my precious angel girl...Lovey xo. (sic)"

Kim's half-sister, Kylie Jenner, 19, also sent birthday wishes to the little girl.

She shared a picture of North and captioned it: "Happy birthday to this cutie."