Ambulance crews have been called to a park in Gravesend after a man was stabbed this afternoon.
Kent Police say they were called at 2.54pm to reports of a disturbance in which a man suffered stab wounds in Woodlands Park.
The air ambulance together with crews from South East Coast Ambulance Service also attended the scene.
SECAMB spokesman Rich Airey said: "I can confirm we have attended following reports of an assault and that the air ambulance service joined us at the scene. One person has been airlifted to a London hospital in a potentially serious condition."
Posting on social media, witnesses said the helicopter had landed there to pick up the victim up from an ambulance, and suggested the stabbing had happened nearby.
They said the victim was seen sitting up in the ambulance, and that obvious stab wounds had not been apparent.
George Daniels, who was at the park with friends, said: "Me and my mates were at woodlands when an ambulance whizzed past the park but initially we didn't think much of it.
"About 10 minutes after, we saw a helicopter hovering above us.
"It landed near the basketball courts and after about another 10 minutes an ambulance pulled up at the entrance to the park and a man was stretchered over to the helicopter.
"It looked like he got up off of the stretcher and was helped into the helicopter by the paramedics and a few minutes later it took off.
"There were crowds of people trying to find out what happened, everyone was shocked and a bit worried."
"We just hoped everything was okay."