A woman in China has been slammed online after she prevented firefighters from breaking the window of her luxury car in order to rescue her trapped three-year-old son.

China's state broadcaster CCTV reported that the incident, which occurred in the city of Yiwu in Zhejiang province last Saturday (July 11), triggered an outpouring of anger on social media.

Large crowds had gathered after hearing the boy's cries of help coming from within the BMW, but were surprised to find his unperturbed mother standing outside the car.

With the boy growing visibly weaker as he clawed in vain against the car window, firefighters attempted to break the window but were stopped by the mother.

An eyewitness said the mother insisted that they wait for a locksmith to unlock the car door as she did not want to damage the car. But the firefighters ignored her and ended up smashing the window to rescue her son.

"It is very dangerous to leave kids inside the car, especially in such heat," one firefighter was quoted as saying.

"The temperature inside the car can soar in a very short time and threaten the child's life."

Netizens expressed shock and disgust at the woman's actions.

One wrote sarcastically: "Looks like the car window is her real son."