Parents have been warned about the dangers of letting children cling to their necks after a second incident captured on video showed a young mother toppling backwards onto her toddler when the youngster cut off the blood supply to her brain.

The short video, taken on CCTV inside the property in Hunan, China, on August 14, shows the young mum in pink with her daughter, also in pink, on her back and holding around her neck as she walks towards the sofa.

But after taking only a few steps, she staggers, appears to stumble backwards and then completely passes out, doing nothing to stop herself as she falls flat on her back and lands on her daughter.

Shockingly, the child's head can be heard striking the tiled floor and she begins screaming almost immediately as the person on the sofa rushes over to help.

The incident follows on from a similar one two months earlier on June 26 inMianyang, in China's Sichuan Province.

A father named Mr Tao was joined by his little daughter as he went to collect a giant hanging poster outside his small business and he carried the girl on his back so he could ensure she would not wander off while finishing the job.

As he stood up, the child did not let go, and a few seconds later, Tao fainted and fell backwards.

He briefly lost consciousness and collapsed on top of his daughter, who began to cry when she realised her father was not moving.

Fortunately, neither of them suffered major injuries, and Tao slowly began to recover.

In both cases, the child cut off the blood supply to the parent's carotid sinus, which briefly caused them to faint.

The carotid sinus is located on both sides of the neck, roughly level with the Adam's apple, about two inches away. It is a blood pressure sensor that regulates the heart and blood vessels when blood pressure rises or falls.

Applying pressure to the carotid sinus can reduce heart rate, lower blood pressure, and even cause fainting. If the pressure is too great or lasts too long, it can be fatal.