Though Netanyahu is expected to win the leadership contest, it is the latest problem for the veteran leader, who after a decade in power, has to lead his party into the third national election since April as the previous two polls did not lead to a conclusive result.
He also faces trial on bribery and corruption charges and though he has dismissed the charges as "politically motivated", there is uncertainty if he will be allowed to contest the next election or be forced to stand down during the trial, with a High Court decision on this expected next week.
Meanwhile, in an embarrassment for Netanyahu, who terms himself the best choice to keep Israel secure, his bodyguards had to escort him off the stage at a campaign rally in Ashkelon on Wednesday night after an air raid siren warning of rocket fire from the Gaza Strip, the BBC reported.
It was the second time that he had been forced to take cover during a campaign rally, following a similar incident in September, it said.
According to the BBC, while Netanyahu is widely expected to retain leadership, he is seeking a decisive win to underscore his influence in the party remains strong.
As the party polls opened on Thursday, Saar, who questions the capability of Netanyahu to lead the Likud - which has been in power since 2009 to another victory - said the time was ripe for change.
"I feel a great awakening (of voters) in the field. People understand that today there is a need for a change and God willing together we will make this change today," he said, according to the BBC.
( With inputs from IANS )