"We are shocked and deeply saddened to learn of the devastating loss of Kelvin Kiptum and his coach, Gervais Hakizimana," World Athletics President Sebastian Coe said in a statement.
"On behalf of all World Athletics, we send our deepest condolences to their families, friends, teammates and the Kenyan nation," the statement said. "An incredible athlete leaving an incredible legacy, we will miss him dearly."
Kiptum was driving his Rwandan coach and a woman in a car near the Rift Valley village where he was born when the accident occurred.
Kiptum and Gervais Hakizimana died at the scene but the woman, Sharon Kosgey, survived with serious injuries and was treated at a local hospital.
"This was a self-involved accident," the newspaper quoted the local police commander, Peter Mulinge, as saying.
Despite the late hour, tributes were paid to Kiptum by senior Kenyan politicians and government officials.
"Devastating news as we mourn the loss of a remarkable individual, Kelvin Kiptum, World Record holder and Kenyan athletics icon," former Kenya prime minister Raila Odinga said on social media platform X.
"My deepest condolences to his loved ones, friends, and the entire athletics fraternity. Our nation grieves the profound loss of a true hero."
Explosive entry
Kiptum, a product of the high-altitude region of Kenya which has produced most of the country's world-renowned distance runners, started his international career on the half-marathon circuit in 2019.
He made an explosive entry into the full 42.195-kilometer distance by running the then-fourth-fastest time on record (2.01.53) to win the 2022 Valencia Marathon on debut.
That race revealed his trademark approach to marathons, running with the pack for the first 30 kilometers and then upping the pace and racing off alone for the remainder of the race.
He used the same tactics to win last April's London Marathon in a course record of 2:01:25 and again in Chicago in October to take 34 seconds off Kipchoge's world mark.
That was to be his final race before his untimely death, which came only a week after World Athletics had ratified his world record.
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Hakizimana, 36, was a former distance runner who still holds Rwanda's record for the 3,000 meters steeplechase. He first met Kiptum when he was training in the Rift Valley and worked with him intensively before last year's London marathon.
"I am shocked and deeply saddened to learn the passing of Kelvin Kiptum and his coach Gervais Hakizimana," Kenya's twice Olympic champion and 800m world record holder David Rudisha said in a post on X.
"This is a huge loss," he said.