Former Israeli prime minister Ariel Sharon, who has been in a coma for eight years, was in a critical condition on Thursday, clinging to life after a decline in the functioning of various bodily organs, his doctors said.

Dr Zeev Rotstein, director of Tel Hashomer hospital, said Sharon's condition had deteriorated over the past two days and a number of vital organs, including his kidneys, were suffering from "critical malfunction".

"He is in critical condition and his life is definitely in danger," Rotstein told reporters. "The feeling of the doctors treating him and also that of the family with him is that there is a turn for the worse."

Sharon's condition had been deteriorating for a long time, he said, but now vital organs were failing.

The former prime minister is not receiving dialysis treatment, as it is not recommended for a patient with multiple organ failure, Rotstein added. Antibiotics had been administered in recent weeks for infections that caused his condition to deteriorate.

"He is receiving all the treatments that a patient in his condition should receive," he said.

Sharon's two sons, Gilad and Omri, and other close family members were at his bedside as doctors warned he may die in hours.

Raanan Gissin, Sharon's former media adviser, said: "The assessment of doctors is that this is a matter of time, of days or hours, that Ariel Sharon will not be with us. This is a very sad moment for me because I was his adviser for over 15 years. And it's a very sad moment also for people in Israel because Ariel Sharon was an icon. He was like [Nelson] Mandela was for people in South Africa."

Under Jewish law, burial should take place as soon as possible after death. However, Israeli officials may seek rabbinical dispensation to delay a funeral to give time for representatives of countries to travel to Israel. US secretary of state, John Kerry, is already in the region for meetings with Israeli prime minister Binyamin Netanyahu and Palestinian president Mahmoud Abbas to discuss the progress of peace negotiations.

A state ceremony is expected to mark Sharon's death, but the former prime minister is likely to be buried next to his wife's grave at the family ranch in the Negev desert.

Sharon, 85, suffered a devastating stroke on 4 January 2006, five years after being elected prime minister. He spent months in hospital in Jerusalem before being transferred to a long-term care facility at Sheba medical centre near Tel Aviv.

Last January, doctors said Sharon had exhibited "robust activity" in his brain during tests. Scans showed Sharon responding to pictures of his family and recordings of his son's voice. However, doctors said the chances of him regaining consciousness were almost zero. Four months ago, Sharon underwent surgery to insert a new feeding tube, through which he receives fluids.

A former military general, Sharon was a hardline rightwinger in political office. But in 2005 he ordered the unilateral withdrawal of Israeli troops and settlers from the Gaza Strip, a move many considered a dramatic change in his political strategy. Within weeks of his stroke, Hamas won Palestinian elections.