Mobile phone footage shows the dramatic moment a shop manager used a tyre iron to break the window of a car to rescue a child trapped in 43C heat.

Video posted to Facebook shows Sarah Oropeza, the manager of a branch of Famous Footwear in Merriam, Kansas, repeatedly hitting the window of a vehicle in a desperate attempt to free a child inside, with the windows and doors all locked.

Talking to KCTV5, Ms Oropeza said around 4:15pm a worker from her shop ran into the store screaming for help: "It was just very, very emotional for all of us that were around."

Ms Oropeza went outside to the car and saw the girl locked inside, dripping with sweat, with her parents or guardians nowhere to be seen. It was over 40C in the Kansan heat.

"The windows were totally up, all the doors were locked, she was covered in sweat...she pulled her hair back and sweat was just drip, drip," Ms Oropeza. "I was just getting so mad that it wouldn't break, and I was just praying, break the window, she is going to die."

It took around three minutes for Ms Oropeza to eventually break open the window and free the child. "She was crying, she was drenched in sweat, he shoes were wet, and I just started crying."

According to Ms Oropeza, the couple caring for the little girl "showed no emotion" when they entered her shop to talk to police after the incident, and they were apparently only concerned with claiming the insurance on their car.