The Leicester City owner’s helicopter has crashed in a car park outside the club’s ground as it left the stadium following a Premier League match.
Vichai Srivaddhanaprabha was in the helicopter when it came down at about 20:30 BST on Saturday, a source close to the family has told the BBC.
One witness said he saw Leicester player Kasper Schmeichel run out of the stadium towards the scene of the crash.
It is not known how many other people were on board the helicopter.
Leicester had drawn 1-1 against West Ham United at the King Power Stadium.
The game kicked off at 17:30 and finished about one hour before the helicopter took off.
Under Mr Srivaddhanaprabha’s ownership, Leicester City won the Premier League in 2016, having started the season as 5,000/1 outsiders
One Leicester season ticker holder, who did not wish to be named, said: “I saw Kasper Schmeichel run out first [from the stadium]and then loads of security guards and stewards.
“I was stood outside the ground but it crashed on the other side.”
Another witness said it appeared “the tail propeller wasn’t working, putting it into a spin”
In the early hours of Sunday, Leicestershire Fire and Rescue Service’s Assistant Chief Fire OfficerAndrew Brodie tweeted that he had just left “multiagency strategic meetings” at Leicestershire Police’s HQ.
He described the crash as “clearly serious and tragic”, adding: “Please don’t speculate on cause or who may be involved. Think of families, friends, responders, and @LCFC and their fans
Freelance photographer Ryan Brown was covering the game and saw the helicopter clear the King Power Stadium before it crashed.
He told BBC Radio Leicester: “The engine stopped and I turned round and it made a bit of a whirring noise, like a grinding noise.
“The helicopter just went silent, I turned round and it was just spinning, out of control. And then there was a big bang and then [a]big fireball.”
Leo Bruka told 5 Live that he saw two police officers whose car was near the crash scene.
“One of them was looking for something and the other one, he ran straight away to the helicopter and he was trying to break the window,” he said.
“Then there is an explosion and they pulled back because the fire was too hot.”
Leicestershire Police said officers were working alongside the other emergency services, the Air Accidents Investigation Branch (AAIB) and Leicester City FC to establish the circumstances of the collision.
In the early hours of Sunday the force tweeted that the AAIB, which said it had sent a team to the stadium, was leading the investigation.
Leicester City said the club was assisting police and emergency services and would issue a more detailed statement in due course.
At the scene
By BBC Sport commentator Ian Stringer
I have seen staff, backroom staff and [the]first team in tears here his evening. The reception area is described as silent, people looking around and crying and not knowing what to do and consoling each other.
I remember the owners taking over. I said hello to them in native tongue, their face lit up. I have generated relationships with them, seen them in Thailand in Bangkok in their home surrounding, they are really nice people.
The chairman looked at me today on the way to the executive box and said “hello and good afternoon”.
We were keeping a close eye on him because of the nature of today’s game and it is really eerie around Leicester at the minute this evening.
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.
Labour MP Jon Ashworth, who represents Leicester South, said he had been in touch with emergency services and thanked them for responding so quickly.
Leicester Mayor Peter Soulsby tweeted that his thoughts and prayers were “with all – particularly owners who’ve done so much for club and our city”.
Former Leicester City and England striker Gary Lineker signed off on Match of the Day by saying it had been a “dreadful day”.
That was the most difficult @BBCMOTD I’ve ever hosted. Thoughts are with everyone at Leicester City. A terrible tragedy. Heartbreaking.
— Gary Lineker (@GaryLineker) October 27, 2018
The thoughts of all at West Ham United are with everybody at Leicester City at this time.
— West Ham United (@WestHamUtd) October 27, 2018
Several Leicester City players, including striker Jamie Vardy, and West Ham have tweeted since the crash.