The Magpas air ambulance has landed near the River Nene to treat a man.
The paramedics were joined by medics from the East of England Ambulance Service at about 2pm to provide care for the man, who had become unwell near Rivergate in the city centre.
Ambulances parked near Asda, while the air ambulance landed in the Railworld car park.
A spokesman for the East of England Amabulance Service said: “We were called at 2pm to Rivergate, Peterborough, to a report of a man who was not breathing.
“An ambulance crew was on scene in under five minutes followed by a rapid response vehicle, ambulance officer and Magpas Air Ambulance.
“They treated a man, believed to be in his 40s, who was in cardiac arrest.
“Following treatment at the scene, the patient was resuscitated and was taken by land ambulance to Peterborough City Hospital in a life-threatening condition.”