Polling stations opened at 7 a.m. to some 6.4 million eligible voters. Polls and partial results showed that Netanyahu — who, if elected, will serve a fifth term in office — has inched past his competitor, a former military chief and leader of the Blue and White political party.
Both political leaders declared victories on Tuesday before races were called.
Gantz voted Tuesday alongside his wife in his hometown of Rosh Haayin in central Israel, where he urged Israelis to vote.
"Go to vote. Choose whoever you believe in. Respect each other and let us all wake up for a new dawn, a new history," he said, telling voters to "take responsibility" for their democracy.
Netanyahu voted in Jerusalem, also alongside his wife, and called voting a "sacred act." If he wins reelection, he would enter his fourth-consecutive term and become Israel's longest-serving leader, following founding father David Ben-Gurion.
The prime minister on Saturday vowed that, if reelected, he would extend Israeli sovereignty over the West Bank. Speaking to Channel 12, he said he was contemplating moves that would put a stop to decades of Israel’s policy recognizing that the lands it seized in the 1967 war would be part of a negotiated settlement with the Palestinians.
The 69-year-old prime minister has been the dominant force in Israeli politics for the past two decades and its face to the world. His campaign has focused heavily on his friendship with President Trump and his success in cultivating new allies, such as China, India and Brazil.
What happens to the land is one of the most contentious issues between Israelis and Palestinians, who argue that the presence of settlements would make a future independent state impossible.
Netanyahu pledged that he would not dismantle a single Jewish settlement and that Israel would retain control of the territory west of the Jordan River, known as the West Bank. More than 600,000 Israelis currently live on the war-won lands and the majority live in the West Bank.
Arab voters appeared poised to play a role in the outcome of Tuesday's election by not voting. Many Arabs, accusing Netanyahu of incitement, were boycotting the election. An hour before polls closed, Arab turnout was at 46 percent, well below the 61 percent turnout nationwide, and Arab political and religious leaders made a last-minute appeal for their followers to vote.
This is a developing story; please check back for updates. Fox News' Talia Kaplan and The Associated Press contributed to this report.