Doctors at the Hadassah Hospital in Jerusalem, where Mr Sharon was rushed from his ranch in the Negev Desert, said that the Prime Minister was on a respirator. There were reports that he had suffered some paralysis.

Prime ministerial powers were transferred to Ehud Olmert, the deputy leader, while Mr Sharon, 77, was undergoing surgery to alleviate pressure on the brain after a cerebral haemorrhage, just over two weeks following his minor stroke. An emergency Cabinet meeting to be chaired by Mr Olmert was scheduled for this morning.

Mr Sharon complained of feeling unwell at the ranch when his personal doctor decided that he should be taken to hospital. There followed delays that left the Prime Minister being taken by ambulance rather than by helicopter to the hospital, losing crucial time. Shmuel Shapira, deputy director of the Hadassah Hospital, said the stroke developed while he was being taken to the hospital, a drive of about an hour.

Dr Shapira told Channel 10 television that Mr Sharon suffered “a massive stroke”, adding: “He was taken to an operating room to drain the blood.”

President Bush said in a written statement that he was praying for the Israeli leader’s recovery. “Prime Minister Sharon is a man of courage and peace,” Mr Bush said. “On behalf of all Americans, we send our best wishes and hopes to the Prime Minister and his family.”

Israel’s chief rabbis and his political opponents said last night that they too were praying for Mr Sharon’s recovery.

The grave nature of Mr Sharon’s condition — just 11 weeks before the general election sparked by his own dramatic split from his ruling Likud Party — threatens not only to disrupt Israeli politics but also to destabilise the whole region.

Mr Sharon had formed a new party, Kadima, to escape the straitjacket of the right-wing activists in Likud who had dogged his every step through the withdrawal from Gaza last summer.

Polls predicted two days ago that Kadima would win most seats in the Knesset, but political analysts said that the party was a “one-man band” whose fortunes could dip dramatically without Mr Sharon. If the new party were to lose him before the election, they said, support could drop by as much as a third, immediately changing the face of Israeli politics.

Kadima’s popularity derived much from Mr Sharon’s strength of character and the hints that he would build on his Gaza withdrawal to set Israel’s borders with the Palestinians and make a concerted effort to reach a final settlement and resolve the conflict.

The main Arab television channels interrupted their programming with news of Mr Sharon’s condition, with al-Jazeera, and even Hamas’s Al Manar station in Beirut hosting live specials monitoring his progress.

Anwar Abu Taha, of Beirut's Islamic Jihad faction, said: “We in Islamic Jihad and all Palestinians have no sympathy for any Zionists whatever . . . Sharon conducted massacres and we have no sympathy.”

In Ramallah people rushed to the streets in celebration on hearing of Mr Sharon’s condition. Cars were honking horns and gunmen took to the streets, shooting wildly in the air and calling others to join their celebrations.

But a Palestinian commentator on the Saudi-owned Al-Arabiya network offered Mr Sharon unexpected praise as “the first Israeli leader who stopped claiming Israel had a right to all of the Palestinians’ land,” a reference to Israel’s recent withdrawal from the Gaza Strip.

“A live Sharon is better for the Palestinians now, despite all the crimes he has committed against us,” said Ghazi al-Saadi.

Haaretz, the Israeli newspaper, commented: “The hospitalisation of [Mr] Sharon will make it difficult for him to return to his job even if he gets through the medical treatment and gets better. Moreover, even if he does recover, he will have a very hard time convincing the public of his ability to serve four more years, after undergoing two strokes in two and a half weeks.”

Doctors said that the blood-thinning medication with which Mr Sharon was being treated after his first stroke may have increased the risk of haemorrhage. Cerebral haemorrhages account for only about 10 per cent of strokes and can result either from rupture of blood vessels or leaking because of too much blood-thinning medication.

“It’s among the most dangerous of all types of strokes,” with half of victims dying within a month, said Robert A. Felberg, a neurologist at Ochsner Clinic, in New Orleans.

The earlier stroke suffered by Mr Sharon — a former general known as “the bulldozer” — had forced aides to contemplate his incapacitation and powers were granted to transfer his authority for 100 days.

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