Multiple videos from the scene show a massive fire at the stadium's vehicle park and emergency services arriving.
Leicester won the Premier League in 2016.
Some fans were still leaving the ground after Leicester City drew 1-1 with West Ham.
Leicester was bought in 2010 by billionaire Vichai Srivaddhanaprabha, who also owns Thai duty-free retail giant King Power.
A Leicester City spokesman said: "The club will issue a more detailed statement once further information has been established".
The footballing community has united to send their thoughts and prayers to those affected by the bad helicopter crash in Leicester.
An East Midlands Ambulance spokesman said: "We received a call at 8.38pm on 27 October to reports of a helicopter crash in the auto park of King Power Stadium in Leicester".
British broadcaster BT Sport was presenting its post-game show in the stadium when the helicopter took off.
A number of Leicester's players, including defender Harry Maguire, tweeted messages with "praying emojis" after the incident. "It turned silent, blades started spinning and then there was a big bang". Just in a spiral. "As far as we are aware nobody around the auto park was caught up in this problem". "I'm shaking like anything".
Photographer Ryan Brown reported hearing the engine stopping after the helicopter cleared the stadium.
This story is developing.
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