Flowers are being laid at the King Power Stadium after the helicopter used by Leicester owner Vichai Srivaddhanaprabha crashed in flames near the 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.
Witnesses said the helicopter seemed to spiral out of control moments after it set off from the stadium at about 8.30pm on Saturday and plummeted into the car park.
The club's owner is known for arriving and leaving the stadium in his helicopter at home games.
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While the BBC has reported a source close to the family as saying that Srivaddhanaprabha was on board the helicopter when it crashed, the police and club have not confirmed who was on board.
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.
Small bouquets were 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.
A small candle was placed in front of the flowers as more people gradually gathered to pray for anybody who may have been on the helicopter.
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 Srivaddhanaprabha is very highly thought of in the city after he bought the Foxes for £39 million in 2010, and became chairman the following February.
Under his ownership the club rose out of the Championship and eventually won the Premier League for the first time in its history in 2015-16, defying odds of 5,000-1.
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.
The website Planefinder said that Srivaddhanaprabha's Agusta Westland AW169 helicopter set off from near Fairoaks Airport in Surrey at about 2.45pm on Saturday, and travelled into Fulham, west London, before turning north and proceeding to the King Power Stadium in Leicester.
A Leicester 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."