The 34-year-old, competing in the mythic race for the seventh time, spun off on the third lap into the safety barriers at the ultra-quick Tertre Rouge bend, demolishing his car.
Le Mans organisers The Automobile Club de l’Ouest issued a statement reporting that emergency services were immediately at the scene to attend the stricken driver.
It continued: “In a serious condition, Allan Simonsen was transferred immediately to the Circuit Medical Centre where he died soon after due to his injuries.
“The Automobile Club de l’Ouest wishes to express its great sadness following this incident, and extends its deepest condolences to the family and those close to Allan Simonsen.”
Simonsen crashed barely ten minutes after the start of the 81st edition of the showpiece endurance event with rain and wind combining to make testing conditions at the Sarthe circuit.
The race was stopped for an hour, the time required to remove wreckage form Simonsen’s car from the track and repair the safety barrier.
The father of one, driving an Aston Martin V8 Vantage, was competing in the GTE-Am category.
His team mates in the No.95 car were his fellow countrymen, Christoffer Nygaard and Kristian Poulsen. Two days ago they had been celebrating taking pole position.
Former Formula One champion Jenson Button led tributes to Simonsen.
The McLaren driver posting on Twitter: “Allan Simonsen RIP.such a tragic loss. A true fighter & a true racer. Safety is something we need 2 improve on in Motorsport.”
Another former F1 champion, Finn Kimi Raikkonen, added: “R.I.P. Allan Simonsen. Sad news.”
Marussia’s Max Chilton wrote: “Truly saddened by the news from Le Mans that Allan Simonsen has passed away after his lap 3 accident”
Simonsen’s team’s website was replaced by a black screen, featuring only the company logo and a statement.
It read: “It is with great shock and sadness that the Aston Martin Racing Team confirms that an accident occurred shortly after the start of the 24 Hours of Le Mans at around 15:09 hrs CET today (22 June) when the No 95 Vantage GTE driven by Allan Simonsen left the track at Tertre Rouge,.
“Aston Martin Racing will not make any further comment until the precise circumstances of the accident have been determined.
“At the specific request of his family, the team will continue to participate in the 24 Hours of Le Mans in tribute to Allan.”
The British constructor’s racing team managing director John Gaw added, “On behalf of all of us at Aston Martin Racing, I would like to extend our deepest sympathies and condolences to the individuals, and families whose friends or loved ones were involved in today’s terrible tragedy”.
Simonsen was the first driver to perish during the race since Austrian Josef Gartner, driving a Porsche, in 1986, and the 23rd overall, including fatalities in qualifying for the race.
Simonsen, who listed Le Mans as his favourite circuit on his personal webpage, was born in Odense, and graduated to endurance racing after starting out as a mechanic.
The 1999 Danish Formula Ford champion’s last success came in April at Silverstone where he won the GT-AM class in the Aston Martin with Poulsen and Nygaard.