Police and ambulance services are currently at a nursery in Sawtry.
The air ambulance is reported to have landed at Sawtry Day Nursery in Fen Lane.
A Cambridgeshire police spokesman said: “We were called at 2.55pm today by the ambulance service after a man in his 40s suffered a cardiac arrest.
“We were called to attend as part of scene maintenance.”
There was no further information about the man’s condition.
A spokesperson for the East of England Ambulance Service said: “We received a call at 2.50pm this afternoon (26th) to reports that a man had collapsed in Sawtry. A paramedic was on scene in two minutes, closely followed by an ambulance, two ambulance officers, and the Magpas air ambulance team. The patient was taken to Peterborough City Hospital by land ambulance, and sadly is thought to be in a life-threatening condition.”
Dawn Quince, early years manager at the day nursery, said: “Yesterday at 2.50pm, staff at Sawtry Day Nursery were called to assist a man who had collapsed on site.
“Nursery first aiders immediately called 999 and began first aid. A paramedic arrived within two minutes and the man was later taken to Peterborough City Hospital in a land ambulance.
“Despite there being lots of activity and several emergency vehicles just outside the nursery, staff did an amazing job shielding the children from the scene.
“Our thoughts and prayers are with this man and his family.”