Actress Greta Gerwig and her director partner Noah Baumbach have welcomed their first child together.

A representative for the Oscar-nominated Lady Bird director confirmed the happy news to multiple outlets on Wednesday (20Mar19) after the couple was spotted pushing a stroller while out and about in New York on Tuesday.

"Noah was pushing and Greta was right next to him. They were chatting and enjoying some fresh air," an eyewitness told E! News. "They were bundled up in the chilly weather and they had a gray and white striped blanket draped over the stroller. It seemed like the baby was sleeping because they were busy talking and didn't have to tend to the baby."

A source also told Us Weekly that they had welcomed a baby boy. The name of the child and when he was born remains unknown.

The tot marks the first child for Gerwig, 35, while Baumbach, 49, has nine-year-old son Rohmer from his marriage to The Hateful Eight actress Jennifer Jason Leigh. The actress filed for divorce in 2010 after five years of marriage and it was eventually finalised in 2013.

Gerwig and Baumbach, who are notoriously private and rarely discuss their relationship, met while working on the 2010 movie Greenberg. She told The New Yorker in 2013 that she was with someone else when she began the movie but called it off when she realised her feelings for Baumach.

The couple, who has since collaborated on films such as Frances Ha and Mistress America, attended the 2018 Golden Globe Awards and the Academy Awards together when Gerwig was nominated for directing and writing Lady Bird.

Gerwig's second directorial effort will be a movie adaptation of Louisa May Alcott's Little Women, starring Saoirse Ronan, Emma Watson and Timothee Chalamet. Production wrapped on the project in December (18). Baumbach is working on an untitled project with Adam Driver and Scarlett Johansson.