The owner of Leicester City was on board his helicopter when it crashed in a ball of flames outside the football club's stadium, Sky sources say.
Witnesses told Sky Sports News the aircraft spiralled then crashed to the ground in a huge fireball in car park E – the club's staff car park which is about 200 metres from the stadium.
The helicopter, understood to be carrying the club's Thai billionaire owner Vichai Srivaddhanaprabha, had taken off from the pitch just moments earlier at around 8.30pm.
Reuters news agency said four other people were also on-board, including Mr Srivaddhanaprabha's daughter, two pilots and a fifth person who has not been identified.
After every home game a number of dignitaries are taken away from the stadium in the helicopter.
Vice-chairman Aiyawatt Srivaddhanaprabha, the owner's son who is known as Top, and the director of football, John Rudkin, were not on-board, according to Sky sources.
Fans who were still leaving the stadium after Leicester City drew 1-1 with West Ham were seen running away as the helicopter came down.
The stadium was evacuated soon after the crash and the area around it was closed off. West Ham's team bus had already left but some Leicester players were still inside the stadium.
A man, who wished to not be named, but has held a season ticket for more than four decades, told Sky Sports he saw goalkeeper Kasper Schmeichel running out of the stadium seconds after the crash before "loads of security guards and stewards".
Many fans remained near the stadium out of concern for those in the helicopter, with a hush having spread through the supporters.
It has not been officially confirmed how many people were in the helicopter or how serious their injuries are, and it is not known whether anyone on the ground was affected.
Footage of the wreckage on Sunday morning showed the helicopter was completely burnt-out.
Sky Sports News reporter Rob Dorsett, at the scene, said: "At about 8.30 this evening, eyewitnesses told me they saw the Leicester City owner's helicopter take off from the pitch inside the King Power Stadium – as it does after every home game – and after a few seconds it appeared to lose control.
"It sounds as if there was a problem with the rear tail propeller which sent it spinning out of control and it crashed into the car park at the rear of the King Power Stadium, just a few hundred metres away from where the pitch is, before it burst into flames."
East Midlands Ambulance Service said it sent a doctor, ambulance and team of paramedics alongside a hazardous area response team to the car park.
Leicester City fan John Butcher told Sky Sports News: "We were facing the ground from the bar across the road, I was with my nephew, we saw the helicopter spinning and it crashed within seconds then burst into flames.
"My nephew was in a real state of shock, he was so upset.
"The Srivaddhanaprabha family means everything to Leicester, they made us champions, you can't ask for more from owners – they won the league for us."
Mr Srivaddhanaprabha was at the helm when the club shocked the football world by winning the 2015-16 Premier League title.
Leicester's star striker Jamie Vardy tweeted eight praying emojis and former Leicester star Gary Lineker tweeted that his "thoughts are with everyone at Leicester City" after the crash, which he described as "heartbreaking".
A spokesman for Leicester City said they were assisting emergency services, adding: "The club will issue a more detailed statement once further information has been established."
The Air Accident Investigation Branch has started its investigation and is at the scene of the crash.
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