Flowers are being laid at the King Power Stadium after the helicopter used by Leicester City owner Vichai Srivaddhanaprabha crashed in flames near the football ground.
The air accident watchdog has launched an investigation into why the aircraft fell to earth in a car park near the stadium a few hours after Leicester drew 1-1 with West Ham.
The club’s owner is known for arriving and leaving the stadium in his helicopter at home games.
The aircraft’s manufacturers said it was the first accident involving one of its Agusta Westland AW169 helicopters.
Italian firm Leonardo Helicopters – formerly AgustaWestland – said it was ready to support investigations into the cause of the crash.
It added: “Leonardo is extremely saddened to hear of the fatal accident yesterday evening involving an AW169 helicopter at Leicester City Football Club’s stadium.
“We wish to offer our sincerest condolences to the family and friends of those involved.
“This is the first ever accident involving an AW169 helicopter.”
The tragedy is being described as the “darkest day” in the club’s history, and mourners began laying wreaths near the stadium on Sunday morning.
Former England and Leicester manager Sven-Goran Eriksson hailed “very, very generous” Mr Srivaddhanaprabha and the “incredible” impact he has had on the club.
Mr Eriksson was the first manager to be hired by the Thai billionaire after he took charge of the club in 2010. And the Swede told BBC Radio Five Live: “It’s frightening news.
“I knew the whole family and the father. When you know him, as i did, you knew he’s a very, very generous man – to the players, the staff and people working for him – with the fans and the community. He’s an extremely generous man.”
Bouquets, flags and football shirts have been left outside the ground by members of the public on Sunday morning alongside a large image of the Hindu god Ganesh which was also propped up in amidst the flowers.
Messages from Leicester fans on the flowers included “In our thoughts!!” and “Thank you xx”.
One fan left a card of a fox with their flowers which read: “Thinking of you all.”
Self-made Thai billionaire Mr Srivaddhanaprabha very highly thought of in the city after he bought the Foxes for £39 million in 2010, and became chairman the following February.
The 60-year-old is also praised for his charity work, donating £2 million towards a new children’s hospital.
Leicestershire Police has said the Air Accident Investigation Branch (AAIB) will now be leading the investigation into the circumstances of the helicopter crash.
The AAIB confirmed on Sunday morning its investigators had been deployed at the site.
A spokesman added: “A team from the AAIB has been deployed to the site and is investigating. Anyone with information that might be helpful to the investigation is asked to contact the police.”
In a statement released in the early hours of Sunday, the police said: “The aircraft came down in a car park near the stadium shortly after 8.30pm yesterday evening (Saturday 27 October) with Leicestershire Police, East Midlands Ambulance Service and Leicestershire Fire and Rescue Service all responding to the incident.
“A cordon is currently in place at the scene to enable the AAIB to examine the area and complete their initial enquiries.
“Leicestershire Police will be supporting the AAIB in its investigation, liaising closely with Leicester City Football Club as enquiries continue.”
East Midlands Ambulance Service said the alarm was raised at 8.38pm and it sent a doctor, ambulance and team of paramedics alongside a hazardous area response team to the car park outside the stadium.
It has not been confirmed how many people were in the helicopter or how serious their injuries are, and it is not clear whether anyone on the ground was affected.
But there are fears that the crash and resulting fireball could have left the pilot and passengers little chance of survival.
One witness told Sky News: “I hope they’re okay. Doesn’t seem like they have had much of a chance. Just burst into flames.”
Witnesses told Sky Sports News the helicopter took off from the pitch but lost control within a few seconds and crashed in the club’s staff car park.
A Leicester City spokesman said: “We are assisting Leicestershire Police and the Emergency Services in dealing with a major incident at King Power Stadium. The Club will issue a more detailed statement once further information has been established.”