Turkmen President-for-life Saparmurat Niyazov has died, a government source told Reuters on Thursday.
"It happened overnight. The president has died," the source said.
"Turkmenbashi (Head of the Turkmen) the Great has died," said a news presenter on Turkmen state-controlled television.
He said the 66-year-old leader had died of a sudden cardiac arrest. The TV ran still images of a national flag in a black-bordered frame.
Niyazov had been in power in his reclusive Central Asian state - the second largest natural gas producer in the former Soviet Union - since 1985 before independence from Moscow.
He tolerated no dissent and enjoyed a flourishing personality cult with thousands of portraits and statues to him throughout the country.
His name has been given to a sea port, farms, military units and even to a meteorite.
A Reuters correspondent in the Turkmen capital said the situation was calm but workers were seen removing New Year decorations from fir trees in the streets.
A spokesman for the Turkmen Embassy in Moscow confirmed the report, saying Niyazov had died.
In 1997, Niyazov underwent major heart surgery in a German clinic and last month he for the first time acknowledged publicly that he had heart disease.
The Turkmen leader created an elaborate personality cult, renaming months and days in the calendar after himself and his family, and ordering statues of him to be erected throughout the desert nation.
Earlier this year, the eccentric leader announced he would provide citizens with natural gas and power free of charge through 2030. Turkmenistan is the second-biggest natural gas producer in the former Soviet Union after Russia.
But he has also tapped the country's vast energy wealth for outlandish projects — a huge, man-made lake in the Kara Kum desert, a vast cypress forest to change the desert climate, an ice palace outside the capital, a ski resort and a 130-foot pyramid.
Niyazov was Turkmenistan's Soviet-era Communist Party boss. Golden statues and busts of the president are scattered across the country, and his portrait is on every bank note and coin, the AP reports.
Prepared by Alexander Timoshik