Caitlyn Jenner and Kim Kardashian have posted tributes to Kylie Jenner following the confirmation that the reality star has had her first child.

The 20-year-old Keeping Up With The Kardashians star announced that she had given birth to a "beautiful and healthy" baby girl on February 1, after months of speculation. 

Now, Caitlyn Jenner has taken to Instagram to mark the happy occasion, posting a photo of Kylie as a baby along with the caption: "My daughter just had a daughter. It's amazing to be by your side through this journey.

"She's so beautiful already. "Can't wait to watch her grow. Throwback to my baby, as a baby."

Meanwhile, Kylie's sister Kim Kardashian, whose daughter Chicago was born in January, posted her own ebullient message on her website, writing: "Mommy Kylie!!! You did it!!!

"I'm so incredibly proud of the woman you have grown up to be and I know that you are going to be the best mom to your new baby girl!

"Our girls are two weeks apart and I can't wait for them to be besties!"

Kylie Jenner holding Kim Kardashian's daughter Chicago, screengrab from Kylie Jenner/YouTube

She added: "I am so proud that you do what you want to do and live your life the way you want, you will pass down all of those amazing qualities to your baby girl.

"You were made to be a mom! I love you!"

Kylie's pregnant sister Khloe Kardashian also congratulated her on becoming a mother, sharing a previously unseen photo of them cradling their baby bumps with the caption: "Congratulations My Sweet Kylie! What a magical ride it's been! I'll miss you bumping along with me.

"Never in a million years did I think we would do this together but it's been that much more special because of it. God is so great!! He had His plan all along!

"I love you little mama, love big mama."

Kylie Jenner accompanied the news that she and boyfriend Travis Scott had welcomed their first baby together with an emotional 11-minute video, captioned "To Our Daughter", that documented her pregnancy journey.

The reality TV star said she wanted to keep her pregnancy a secret as she wanted to "prepare for this role of a lifetime in the most positive, stress-free and healthy way" that she could.

She said: "I'm sorry for keeping you in the dark through all the assumptions. I understand you're use to me bringing you along on all my journeys. My pregnancy was one I chose not to do in front of the world.

"I knew for myself I needed to prepare for this role of a lifetime in the most positive, stress-free and healthy way I knew how. There was no gotcha moment, no big paid reveal I had planned.

"I knew my baby would feel every stress and every emotion so I chose to do it this way for my little life and our happiness."

"Pregnancy has been the most beautiful, empowering and life changing experience I've had in my entire life and I'm actually going to miss it," she continued.

"I appreciate my friends and especially my family for helping me make this special moment as private as we could.

"My beautiful and healthy baby girl arrived February 1st and I just couldn't wait to share this blessing. I've never felt love and happiness like this I could burst. Thank you for understanding."