The Uzbek government did not immediately confirm the reports. Earlier on Friday it said the health of Karimov, who has been in hospital since last Saturday, had sharply deteriorated.
“Yes, he has died,” one of the diplomatic sources said when asked about Karimov’s condition.
Long criticized by the West and human rights groups for his authoritarian style of leadership, Karimov had ruled Uzbekistan since 1989, first as the head of the local Communist Party and then as president of the newly independent republic from 1991.
Karimov did not designate a successor and analysts say the transition of power is likely to be decided behind closed doors by a small group of senior officials and family members.
If they fail to agree on a compromise, however, open confrontation could destabilize the nation of 32 million that has become a target for Islamist militants.
Uzbekistan is a major cotton exporter and is also rich in gold and natural gas.
A hint at who is going to succeed Karimov may come with the government’s announcement of his death – which one source said was expected later on Friday – and whoever it names to head the commission in charge of organizing the funeral.
The latter appeared likely to take part in Karimov’s hometown of Samarkand where his mother and two brothers are buried. Municipal authorities there mobilized public workers to clean the central streets late on Thursday.
A source in the government of neighboring Kazakhstan told Reuters on Friday that Kazakh President Nursultan Nazarbayev planned to cut short his visit to China and travel to Uzbekistan on Saturday.
Among potential successors are Prime Minister Shavkat Mirziyoyev and his deputy Rustam Azimov. Security service chief Rustam Inoyatov and Karimov’s younger daughter Lola Karimova-Tillyaeva are also players who could become kingmakers.