A leading pro-government lawmaker called on Israel's Supreme Court to dismiss petitions against a key plank of the government's controversial judicial reforms, saying Tuesday's hearing was harming "the soul of Israel's democracy".

A full 15-judge panel of the top court convened to hear petitions to strike down amendment of the so-called "reasonableness doctrine" that the government of Prime Minister Benjamin Netanyahu passed through parliament as a basic law in July.

Since the judicial overhaul was first unveiled in January, Israel has been rocked by mass street protests that have divided the nation.

The amendment limits the powers of the court to review and sometimes overturn government decisions, which opponents say paves the way to authoritarian rule.

Dozens of noisy demonstrators gathered outside the court building Tuesday, banging drums, blowing whistles, chanting and waving Israeli flags.

Chief Justice Esther Hayut said there were eight petitions filed against the legislation limiting the "resonableness doctrine".

"It's clear you think that the duty to act reasonably applies to the government and its ministers," Hayut said, addressing a lawyer representing parliament.

"But who makes sure they indeed do so?"

Pro-government lawmaker Simcha Rothman, who as head of the Constitution, Law and Justice Committee proposed the amendment in parliament, told the court the hearing was "a failure" in itself.

"Why do we even need a legal procedure or ruling that will harm the soul of democracy?" he asked.

"For years, in a gradual process of sophisticated legal arguments, the Israeli court gave itself unprecedented authorities," he said, arguing there was no "justification" for the court to rule on a government's functioning.

'Only' protection

Lawyer Ilan Bombach, who is representing the government, told reporters that if the court intervened in "basic laws" then "we won't be the same democratic country we used to be".

But protester Batia Cohen said it was the actually the government that was out to "destroy democracy" in Israel.

"This is the only country that I have and I have children, grandchildren, and I'm fighting for them," said Cohen, 63, who had travelled to Jerusalem from the northern port city of Haifa.

"They (government) want to be above law, so the only one that protects us from them is the court."

Opposition leader Yair Lapid said on Facebook that the amendment was an "irresponsible document" in itself.

Netanyahu's administration, a coalition between his Likud party and extreme-right and ultra-Orthodox Jewish allies, insists that the legal changes are needed to rebalance powers between elected officials and the judiciary.

Justice Minister Yariv Levin, the main architect of the reforms, said the hearing was a "fatal blow" to democracy, since for the first time the court was considering striking down a basic law, legislation that in Israel takes the place of a constitution.

"The court, whose judges select themselves behind closed doors and without a record, is placing itself above the government, the parliament, the people and the law," he said in a statement.

"It means that the court has no checks and balances. It's a single ruler."

'No authority'

Government supporters who also gathered outside the court expressed their backing for the amendment and for Netanyahu.

"I think the Supreme Court judges need to say we don't have the authority to intervene in basic laws," said Jerusalem resident David Kozlovsky, 31.

"I hope that the government will be able to make the democratic reform in the Supreme Court and also those (economic) reforms that are very critical for Israel."

Israel does not have a constitution or upper house of parliament, and the "reasonableness doctrine" was put in place to allow judges to determine whether a government had overreached its powers.

The Supreme Court used the measure in a recent high-profile ruling which barred Aryeh Deri, a Netanyahu ally, from serving in the cabinet because of a tax evasion conviction.

He rejects the accusation.