This is the dramatic moment a heroic bystander risks his life by dashing down a collapsing escalator to press the stop switch and save a woman from being swept to certain death.

The video footage was captured at a supermarket in Fengxian, in Shanghai, China, on April 4, and shows one woman looking at her mobile phone while another comes under the escalator in order to be taken up to the next level.

But shortly after stepping onto the device, it collapsed under her feet, leaving her body half wedged inside the device with her being dragged slowly but surely towards the top where experts said she would almost certainly have been crushed to death as she was pushed against the floor above.

There were also mechanical parts at the top that were waiting to snare the woman if the device had not been switched off in time.

The woman who was at the bottom and was on her phone rushed over to try and find the stop button when she realised what was happening, but in her panic was unable to do so.

She also does not want to step onto the escalator which could also have collapsed further and allowed her as well.

Fortunately, a man further up the escalator who saw what happened ran down and over the damaged section where he was unable to press the off switch and stop the escalator moving.

Although she survived and was taken to hospital, the woman's husband Mr Lu said that her leg was badly damaged and is still not clear whether medics will be able to save it following the incident.

A spokesman for the supermarket which has since been closed after the accident blamed a malfunction in the escalator but local health and safety officials are working with police to identify those responsible and identify if there are other safety hazards as well as prosecute anybody if negligence is found.

The woman was eventually freed from the escalator by firemen who had to wait for experts from the manufacturer of the company.

They had to unscrew large sections of the escalator and also used hydraulic claws to lift other parts away in a mission that lasted almost an hour.

The footage was shared by the woman's angry husband who pointed the finger of blame at incompetent and careless supermarket officials for allowing the faulty device to carry passengers.