Polls for Israel's second parliamentary election in five months suggest that the outcome is too close.
Former military chief Benny Gantz's centrist blue-and-white coalition is expected to hold between 32 and 34 seats, and Premier Benjamin will win Netanyahu's right-wing Likud party with 31
Former Defense Minister Avigdor Lieberman could become kingmaker.
Mr. Netanyahu called the quick referendum after forming no governing coalition after a April election.
Negotiations on the formation of a new coalition are expected to start as soon as the preliminary results are available on Wednesday morning.
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According to a survey by Israeli public broadcaster Kan, Likud and Blue and White would each receive 32 seats in the 120-seat Knesset.
This was followed by the Israeli-Arab joint list with 12 seats. The nationalist Yisrael Beitenu party of Mr. Lieberman at 10; the right-wing Yamina party at seven; the ultra-Orthodox Shas and United Torah Judaism parties with nine and eight respectively; and the alliances of the Left Democratic Union and the Labor Gesher, each with five. Channel 12 News placed 34-seat Blue and White and 33-seat Likud in the lead, while Channel 13 News predicted Blue and White would win 33 seats and Likud 31.
Surveys showed that neither Mr. Netanyahu or Mr. Gantz could form a governing coalition without the support of Mr. Lieberman.
He prevented Mr. Netanyahu from forming a coalition after the last election because he refused in a long-standing dispute with religious parties over a bill on exemption from compulsory military service for ultra-orthodox young men.
During the campaign for this vote, Mr. Lieberman stated that he wanted a unity government in which Likud would share power with Blue and White, something Mr. Netanyahu has ruled out.
If the official results prove inconclusive, it will be up to President Reuven Rivlin who gets the mandate to form a government. This person has 28 days to spare, with a possible extension of no more than 14 days.