Stunned Leicester City fans have gathered at the club's ground after its owner's helicopter crashed and exploded outside the stadium.
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.
Witnesses said they saw it just clear the stadium before it spiralled out of control and crashed in a fireball.
The BBC understands two crew members and three passengers were on board.
Leicester had drawn 1-1 against West Ham United at the King Power Stadium, with the match finishing about one hour before the helicopter took off from the pitch.
Under Mr Srivaddhanaprabha's ownership, the club won the Premier League in 2016, having started the season as 5,000/1 outsiders.
Season ticket-holder Richard Jackson, 53, from Market Bosworth, Leicestershire, travelled to the stadium to join with other fans.
"I'm just devastated really, it is such a tragedy you don't expect to happen," he said.
"These owners have been absolutely fantastic, probably the best owners in the whole English system."
Former Scotland winger Pat Nevin said the owners were popular with Leicester's supporters.
The football pundit said: "Whenever Leicester fans rang in to gripe about the team, they were never aimed at the owners."
Minute's silences were held ahead of the Premier League matches between Burnley and Chelsea, and Crystal Palace and Arsenal.
Leicester City said it was assisting police and emergency services and would issue a more detailed statement in due course.
At a ceremony to mark Diwali, City Mayor Peter Soulsby said: "The news sent shudders through the whole of the city.
"It's a chance to reflect on that tragedy and how much has been given to this city by the owners.
"We have a lot to thank them for.
"It is important we go ahead with tonight's event. It's a time of darkness so it is appropriate we celebrate the triumph of light over darkness."
Richard Mobbs, from Burton Overy in Leicestershire, said he last saw the chairman in June when they discussed a player who was about to join the club.
"I spoke to Vichai a lot," the 68-year-old said.
"It is such a shock. You just have to pay your respects."
Mr Mobbs described Mr Srivaddhanaprabha as a "lovely, quiet, down to earth man", and paid tribute to his family.
"They are all friendly," he said.
"This season they bought me a season ticket."
Anupat Maturongpituck, a student from Thailand studying at the University of Leicester, came to the King Power Stadium on Sunday to "pay my respects", adding news of the crash has had a "great impact" in Thailand.
Freelance photographer Ryan Brown, who was covering the game, 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."
Leicester boss Claude Puel expressed his sadness after the incident and moved to reassure those that may have been worried he was not on board the helicopter.
He told Radio France: "It's a tragedy for the club.
"I think very strongly about the victims and their families, and I wanted to reassure everyone who cares about me, I'm terribly sad but I'm fine."
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."
A Leicester season ticket holder, who did not wish to be named, said he saw goalkeeper Kasper Schmeichel run out from the stadium followed by "loads of security guards and stewards".
"I was stood outside the ground but it crashed on the other side," he said.
Another witness said it appeared "the tail propeller wasn't working, putting it into a spin".
Andrew Brodie, assistant chief fire officer at Leicestershire Fire and Rescue Service, said the crash was "clearly serious and tragic".
He tweeted early on Sunday that he had just left "multiagency strategic meetings" at Leicestershire Police's HQ, and asked for people not to speculate on the causes or people involved.
"Think of families, friends, responders, and @LCFC and their fans," he said.
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.
Nick Rushton, leader of Leicestershire County Council, said he was "deeply concerned" by the crash, and paid tribute to emergency services staff for their "professional response".
Labour MP Jon Ashworth, who represents Leicester South, said he had been in touch with emergency services and thanked them for responding so quickly.
The aftermath of the crash
By Ian Stringer, BBC Sport commentator
It is really eerie around Leicester at the minute.
I have seen staff, backroom staff and the first team in tears here this 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".
He donated millions of pounds to Leicester Royal Infirmary, and also gave money to the University of Leicester.
He's taken Leicester into his own heart - it's a hugely important place for him that he's made home. It's a one-club city here in Leicester, and we've welcomed him with open arms.
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".
Mark Kent, the former British ambassador to Thailand, said he was "shocked" to hear of the crash, adding that he had celebrated Leicester's 2016 title win with the club's chairman.
Very shocked to see the news of the helicopter crash in Leicester. I knew Khun Vichai and his family during my time as Ambassador in Bangkok. I celebrated the Premier League title with them in 2016. My thoughts are with them now— Mark Kent (@KentArgentina) October 28, 2018
A match between Leicester City Women and Manchester United Women that was set to take place on Sunday was postponed.
Former Leicester City and England striker Gary Lineker signed off on Match of the Day by saying it had been a "dreadful day", while BT Sport's Jake Humphrey - who was broadcasting from the King Power Stadium - said it was the "single hardest moment" of his career.
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
Our thoughts are with all at @LCFC following the major incident after their game at the King Power Stadium tonight.— The FA (@FA) October 27, 2018
In 21 years, delivering this news live, with little information was the single hardest moment. You can see the shock.— Jake Humphrey (@mrjakehumphrey) October 28, 2018
The BT Sport team remained professional, yet all our thoughts were, and remain with, everyone at @LCFC a genuinely special family club xxhttps://t.co/oOCWKmcQVo
Several current and former Leicester City players, including striker Jamie Vardy and ex-England goalkeeper Peter Shilton, and West Ham have tweeted since the crash.
🙏🏼🙏🏼🙏🏼🙏🏼🙏🏼🙏🏼🙏🏼🙏🏼— Jamie Vardy (@vardy7) October 27, 2018
Witnessed the crash @LCFC last night with my wife. Absolutely devastated and in shock our thoughts and prays are with everybody involved and Leicester City 🙏— Peter Shilton (@Peter_Shilton) October 28, 2018
🙏🏿 this man brought back the good days back to lcfc and the city of Leicester. What he’s done for the club and the City has been AMAZING, such sad news. 🙏🏿 @ King Power Stadium https://t.co/y9BbP8L55c— Emile Heskey (@EmileHeskeyUK) October 28, 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
- Father of four
- Billionaire and founder of duty-free consortium King Power International
- Ranked as the fifth richest person in Thailand by Forbes Magazine
- Bought Leicester City in 2010 for £39m
- Under his ownership, the club won the Premier League in 2016 and reached the Champions League quarter finals a year later