A child has reportedly died of heatstroke after he was left in a car for up to 12 hours after his mother attended a party.

Three-year-old Vicente was found unresponsive in a locked vehicle parked outside of his home in Mexicali, Mexico, just south of the US border, according to The Sun.

His mother reportedly told investigators that she returned from a party about midnight on Friday and forgot about her son in the car.

Emergency services were contacted by a neighbour who noticed the boy in the car about 1.30pm on Saturday, local time.

When they arrived, a woman was carrying the child and claimed he was unresponsive.

After being treated by firefighters and paramedics, Vicente was declared dead at the scene.

Forensic experts determined the boy had suffered from severe heat exposure.

It is believed he died between 9am and 10am, when temperatures were above 33C.

Forensic Medical Service head Cesar Gonzalez Vaca said an autopsy found no signs of physical violence, however, burns were found on the child’s arms and legs.

An investigation has been opened into Vicente’s death by prosecutors from the Baja California State Attorney General’s office.

There are calls from locals to have the incident investigated as a possible case of neglect.