Sky Sports News reporter Rob Dorsett said the helicopter took off from the pitch, as it does after every game.
He said that after a few seconds it appeared to lose control and crashed into the car park just a few hundred metres away.
One witness said it appeared "the tail propeller wasn't, working putting it into a spin".
Freelance photographer Ryan Brown was covering the game and saw the helicopter clear the King Power stadium before it crashed.
He told 5 Live: "Literally the engine stopped and I turned around, and it made a bit of a whirring noise.
"It turned silent, blades started spinning and then there was a big bang."
He said when he ran to the scene "there was a huge fireball" and it looked like the helicopter had crashed in an industrial park next to the stadium.