A man has been arrested after CCTV footage captured a sickening attack on an unsuspecting rail worker in Hong Kong.

The footage, which has since gone viral on social media, shows a 59-year-old female cleaner standing on the platform at a station in Yuen Long, Hong Kong.

A man walks behind her and, without hesitating, gives the cleaner a powerful shove in the back — sending her flying onto the train tracks below.

The attack happens so quickly, the cleaner is not able to put her arms up to shield her fall.

As the cleaner lies motionless on the tracks, the man continues walking calmly along the platform, not looking back.

The South China Morning Post reported that a 56-year-old man was arrested near the railway station on suspicion of the assault.

No trains were approaching the station, and the cleaner was rescued from the tracks and taken to hospital.

“The woman suffered injuries to her jaw and was sent to Pok Oi Hospital for treatment,” a police spokeswoman told the Post.