Demonstrations have reached a fever pitch across Israel as the Knesset begins the process of enacting a law that will reduce the power of the judiciary to scrutinise government decisions.

On Sunday morning, the Israeli parliament started to debate deeply controversial legislation that will end legal scrutiny of whether decisions made by ministers are “reasonable”.

The bill is expected to become law early next week, a step that supporters say would prevent unelected judges from determining government policy, but opponents claim would cripple Israeli democracy.

Hundreds of thousands of protestors rallied across the country to express their opposition to the legislation on Saturday night, after 10,000 reservists announced they would halt their volunteer military duty.

Despite temperatures of around 33 degrees, a miles-long column comprising tens-of-thousands of demonstrators marched into Jerusalem on Saturday evening.

Carrying Israeli flags and singing the national anthem, they marked the high water mark of months of demonstrations. 

Demonstrators wave Israeli national flags

Demonstrators wave Israeli national flags (Photo: Getty)

Organisers claim half a million Israelis took part in the protests nationwide, though this could not be independently verified, the Times of Israel reported.

The ruling coalition is pressing ahead with judicial reforms despite Prime Minister Benjamin Netanyahu undergoing surgery on Sunday morning to have a pacemaker fitted.

The operation came a week after the Likud leader was admitted to hospital over a reported case of dehydration, during which he was fitted with a heart monitoring device.

In a statement released on Sunday, Netanyahu said: "A week ago I was fitted with a monitoring device. 

"That device beeped this evening and said I must have a pacemaker and that I must do this already tonight. I feel great, but I need to listen to my doctors."

Roy Beinart, who manages the arrhythmia centre at Sheba Medical Center, said: "The implant went smoothly without any complications.

“He is not in a life-threatening condition and he feels great and is returning to his daily routine."

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Israelis rallying at the western wall in Jerusalem's old city pray for national unity over the government's judicial overhaul bill (Photo: Getty Images)

Dozens of security chiefs have meanwhile written to the prime minister backing striking military reservists and calling on him to halt the judicial reforms for compromise talks.

An open letter signed by former heads of the IDF, Mossad and Shin Bet compares Israel's current crisis to "the eve of the Yom Kippur War".

It says: “The legislation is shattering the common foundation of Israeli society, tearing the people apart, dismantling the IDF and causing grievous harm to Israel’s security.

“The legislative process is violating the social contract that has existed for 75 years between thousands of reserve commanders and soldiers…

“We expect you to take responsibility… Stop the legislation and begin a process of talks with changes to be made only under broad consensus among the people and in the Knesset.”

Netanyahu’s former Mossad chief, Yossi Cohen, has urged the prime minister to stop the reforms “in the face of the Iranian threat”.

Writing in the Yedioth Ahronoth daily newspaper, he said: "at this critical time when the Iranian threat looms from multiple fronts, we must ensure that Israel's security resilience remains uncompromised."

An aerial view shows protesters attending a march in Tel Aviv

An aerial view shows protesters attending a march in Tel Aviv in Saturday (Photo: Getty)

Netanyahu, he added, should launch, "urgent and immediate dialogue between the various groups representing different opinions, aiming to reach a shared national consensus, which has been instrumental throughout Israel's existence."

In Tel Aviv, around 170,000 demonstrators converged on Kaplan Street, Haaretz reported, which has become a locus of dissent over the past months.

“I think this is the only place to be right now,” one protesters marching into Jerusalem told the New York Times. 

“Not at the beach and not in the air-conditioning. Here you see the people of Israel at their best. It’s terribly hot, but they are marching on.”