An NHS worker was left unconscious after being subjected to a "totally unwarranted violent assault" on a bus that was "triggered by face masks".

CCTV footage shows a man repeatedly punching the 63-year-old victim to the floor before stamping on his head five times, leaving him unconscious.

The incident happened onboard the 149 bus just before it stopped at Seven Sisters station in north London at around 9.45 pm on 23 August, the Metropolitan Police said.

Detectives say the victim, an NHS track and trace worker, boarded the bus via the middle doors before the suspect.

Five minutes later, the suspect followed the victim towards the back doors, where police believe he had gone to try and create some distance between them.

#APPEAL #SHARE | Police have released CCTV of a man they want to trace after a confrontation over face masks led to a 63yo NHS worker being assaulted & left unconscious on a bus in north London.

Can you help us trace him?

101 ref CAD 7981/23Aug.https://t.co/Fvrj2EM992 pic.twitter.com/EulIH396kJ

— Metropolitan Police (@metpoliceuk) September 18, 2020

The suspect is thought to have "taken offence" when the victim moved away from him because he wasn't wearing his mask properly, the investigating officer said.

PC Bowman, of the roads and transport policing command, said: "Although there is no sound on the CCTV and all the victim remembers is waking up in hospital, we believe that this was all triggered by face masks.

"We think that the attacker, who had his face covering beneath his chin, took offence when the victim, who was fully covered, consciously moved away from him.

"When the attacker then follows the victim to the back of the bus, he can be seen pointing and gesturing at the victim's face mask before he starts repeatedly punching and kicking him.

"This was a totally unwarranted violent assault and we urgently need to speak to this man."

The suspect is described as a tall black man aged approximately between 23 and 25, tall, with an athletic or muscular build.

He was wearing blue tracksuit bottoms, a white vest and white trainers.