The Knocked Up actor, who was out with his girlfriend Alexandra Hoffman, tweeted that he saw a woman go into labour right next to him and began taking pictures.
"Craziest thing I've ever seen. A woman have (sic) birth next to me in a park," he said. "I took a picture of the placenta and TMZ caught me. Embarrassing."
TMZ later posted a picture of Hill peering at the bench where the woman was sitting before she was taken to hospital.
"We randomly noticed Jonah snapping a cell phone pic of the birthy aftermath near the bench where the woman was sitting when she went into labour," they wrote.
"We tried to ask Hill about the situation... but he seemed a little too embarrassed to talk... We don't blame ya for taking pictures, J. It's not like that kinda stuff happens every day."
Hill stars alongside Leonardo DiCaprio and Jamie Foxx in Quentin Tarantino's forthcoming film Django Unchained. The western, which also stars Samuel L Jackson, is due to be released in the UK on January 18, 2013.
Watch the trailer for Django Unchained below: