A 13-year-old boy was killed by a low-clearance sign after he stood up through the sunroof of a moving car in southern China.

Shocking video filmed by a stunner onlooker from a vehicle following behind shows the boy sticking out of the car as it drives along a highway.

However, the car does not slow down at all when it is passing the low-clearance sign and the boy is knocked sideways by it.

The incident occurred in Xinyu City in southeastern China’s Jiangxi Province on October 28.

Newsflare has edited the video to avoid showing the very disturbing moment of death.

The onlooker can be heard saying: “It is near the low-clearance sign now. If he's knocked into it, he will definitely die.

"Have they seen the clearance sign?" he asks.

"God, he really hit on it!” he later says.

According to reports, the car driver was not the boy’s relative and his guardians were in another car behind him.

The boy was killed on the spot. The case was being investigated.

This is the terrifying moment a 13-year-old boy was killed by a low clearance sign after he stuck his body out of the sunroof of a car in southern China.