Embattled Israeli Prime Minister Benjamin Netanyahu has declared victory in a leadership primary in his right-wing Likud party, ensuring he will lead it in March elections.

"A huge win! Thank you to Likud members for their trust, support and love," Mr Netanyahu tweeted an hour after polls closed.

Initial results showed he comfortably beating rival Gideon Saar, though a final tally was expected to take several hours.

An exit poll cited by the political correspondent for Israel's Channel 12 news predicted that Mr Netanyahu would retain the right-wing party's leadership with 71.52% of votes.

A defeat for Mr Netanyahu, Israel's longest-serving premier, would be a major shock, but even a relatively close victory could weaken his influence over the right-wing party he has dominated for 20 years.

After a decade in power, the 70-year-old has recently been damaged by a series of corruption indictments.

The winner will lead Likud into a third general election within 12 months in March, after previous elections last April and September had seen it deadlocked with the centrist Blue and White party and neither one able to form a government.

With storms lashing the country, early indications suggested turnout would be low - prompting Mr Netanyahu to issue a plea to voters.

"Everything is within reach, but only if you get out to vote," he said on Twitter.

"The low percentage of turnout hurts us."

His Facebook page showed a live video of him working the phones calling voters.

Mr Saar, 53, a former interior and education minister, is seen as slightly to the right of Mr Netanyahu and has called for an even more hawkish policy towards Palestinians. 

Mr Saar called it a "fateful day" for the party and the country, speaking as he went to vote near Tel Aviv. 

"We can win today and embark on a new path, which will enable us to form a strong and stable government," he said.

Mr Netanyahu cast his vote in a booth set up in his residence, while Mr Saar visited a polling station near the commercial capital Tel Aviv.

The election comes after a troubled year for Israeli politics and the premier.

General elections in April and September saw Mr Netanyahu deadlocked with centrist challenger Benny Gantz, neither of them able to command a majority in Israel's parliament.

Last month, Mr Netanyahu was indicted for fraud, bribery and breach of trust in three corruption cases, allegations he strongly denies.

Mr Netanyahu has sought to paint himself as an irreplaceable leader fighting a "witch hunt" by the police, the legal establishment and the media.

The primaries were called shortly after the charges were issued.

A series of polls in recent weeks have indicated a Saar-led Likud might win fewer seats in a third election than under Mr Netanyahu, but the overall right-wing bloc might be larger - potentially yielding a viable governing coalition.

Mr Saar has not attacked Mr Netanyahu personally and even hinted that he would support him to become Israel's president, a largely ceremonial role.

Mr Netanyahu's downfall has been predicted multiple times since he became premier for a second time in 2009, but he has defied expectations and appears determined to fight on.

Under Israeli law, a prime minister is only forced to step down once convicted with all appeals exhausted.