A four-month-old infant was found dead after she was left inside a vehicle for most of the day in Oklahoma. Her grandmother had thought she had left the girl at a daycare centre before going to work.

"She apparently had thought that she dropped off the child this morning, which she had not," Mark Opgrande, a spokesman with the Oklahoma County sheriff's office told KFOR news channel.

"After she got off work, she drove back to Luther to stop by the child care centre.

"They informed her that she did not drop off the child and they went, proceeded to look for the child inside the daycare. They couldn’t find her. That’s when they went out to the vehicle, and then discovered her outside in the back of the car. She was deceased."

The fire department was called to Apple Creek Learning Centre in Luther at around 5.30pm on Friday. The four-month-old was found still inside the vehicle and pronounced dead at the scene.

The grandmother, whose name has not yet been released, is being interviewed by police investigators at the Oklahoma County Sheriff's Office who will prepare a report and send it on to the attorney’s office.

"She’s being questioned, she’s obviously distraught, this is a tragic situation and that’s why we remind parents all the time. It’s hot out and things like this aren’t supposed to happen, but they do.”

The grandmother has custody of the baby. No charges have so far been filed.

A Facebook post by the daycare announced news of the baby’s death: “We have some very very sad news from Apple Creek. A tragic accident with one of our beloved babies. I ask everyone to pray for this precious family. Please. Nothing happened AT Apple Creek but it did occur in our parking lot.”

Every year, around 37 children die in the US after being left in a car, according to Kids and Cars. The safety organisation said that the month of July was a record high for hot car deaths. This year, 29 children died of heatstroke in the US after being left in a car.

This represented "the highest we’ve ever had,” said Jan Null a meteorologist with the Department of Meteorology & Climate Science at San Jose State University. He has logged the statistics on the No Heatstroke website.The previous record as of 31 July was 28 deaths in 2010. Null explained it was “a year where we ended up with 49 deaths for the year.”