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.
Image copyrightRex FeaturesImage caption Smoke coming from the crash site Image copyrightPete White Image caption The helicopter shortly after taking off this evening
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