Fredys Soccaras, mayor of Valledupar, the city where the singer-songwriter lived, told Caracol radio that Diaz died yesterday of a heart attack after being rushed to a hospital.
From a poor childhood on a farm near Colombia's Caribbean coast, Diaz rose to become one of the top-selling artists of the musical genre revered throughout Colombia. He was honoured with a Latin Grammy for best vallenato album in 2010.
Diaz was also known for his off-stage excesses, including a lifelong battle with drugs and alcohol and a conviction for trying to cover up the overdose death of a fan at his home.