The 77-year-old Sharon was placed in a deep coma after undergoing seven hours of surgery before doctors were able to halt bleeding in his brain but he remained in a critical condition.
Some of the prime minister's closest allies said that his life remained in danger and acknowledged that he was unlikely to ever be able to return to office.
Palestinian leaders expressed fears that Sharon's departure from the political scene would leave a massive void and could plunge the region into more bloodshed.
"His condition is still serious but he is stable," Shlomo Moryussef, director of Jerusalem's Hadassah hospital, said in a bulletin to reporters.
"All the parameters that we are monitoring are as expected after an operation of this type.
"Part of the treatment is to keep the [blood] pressure in his cranium low through a deep coma and ventilation for at least the next 24 hours."
Two of his closest allies, transport minister Meir Sheetrit and the leader in parliament of his Kadima party, Ronni Bar-On, both confirmed the gravity of the situation by saying that the prime minister was "fighting for his life".
Haim Ramon, an MP who joined Kadima from the center-left Labor party, acknowledged that Sharon was unlikely to return to work.
"I pray that he will recover, but it seems to me that he will not be able to exercise his functions as prime minister any time soon or perhaps ever."
The powers of the premier, who is seeking reelection in a nationwide poll scheduled for March 28, have been transferred in the short-term to finance minister and Deputy Prime Minister Ehud Olmert.
Sharon's late night admittance came hours before he was due to undergo a procedure to repair a small hole in the heart to prevent a repeat of a minor stroke he suffered on December 18.
His precarious state of health will upset all previous predictions of the outcome of the election in which Kadima had been expected to romp to victory, with commentators already declaring an end to the Sharon era.
Officials, however, dismissed any suggestion that the election be postponed.
Sharon's second stroke also comes amid rising chaos in the Palestinian territories ahead of a January 25 legislative election that will also have far-reaching consequences for the Middle East peace process.
Olmert told an emergency cabinet meeting that it was important that the country did not come to a standstill.
"We are all praying for the prime minister. We are living with a difficult and complex situation but the government is functioning and Israel is functioning."
US President George W. Bush, who urged the overweight Sharon to go on diet after his first stroke, sent his prayers for a man that he hailed as "a man of courage and peace".
There was also a get-well message from Palestinian Prime Minister Ahmed Qurei.
"This is a major event which will have repercussions not just in Israel but in the whole region," Qurei told reporters.
"The Israelis are lamenting the loss of Sharon, their leader and their decision-maker."
He expressed hope that whoever now emerged as the new Israeli leader after the March election would be someone "who wants peace and is ready to negotiate with the Palestinians".
Chief negotiator Saeb Erekat said that he feared that the Palestinians could end up as the unwitting victim of a post-Sharon power battle.
"The Palestinian people risk being made to pay the price of the battle for power in Israel with an intensification of settlements and assassinations."
Sharon's spokesman Ranaan Gissin said that Israel's enemies should not seek to exploit the turmoil, warning Palestinian militants and the Lebanese militia Hizbullah "not to entertain any notion that they can start any escalation".
"This is not the time to mess with us," said Gissin.
But Islamist movement Hamas was shedding few tears for its archenemy, with chief spokesman Sami Abu Zuhri declaring that "the world is on the verge of being rid of one of its worst leaders".
Few of Israel's prime ministers have left such a mark on both the military and political landscape as the controversial Sharon over the last half a century.
Sharon, who transformed from an ultra-hawk to a man regarded as a peacemaker, and his party have been riding high in the opinion polls, forecast to emerge as the largest party after the election.
However, although Sharon has been able to attract other heavyweights such as Olmert from his old rightwing Likud party, his new party is seen as largely a one-man band with few concrete policies or party institutions.
His exit will not only be a blow to Kadima's prospects but could also revive the prospects of Likud, now led by Sharon's hawkish rival Binyamin Netanyahu.
© 2005 Agence France-Presse
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