(CNN) Preliminary exit poll estimates released by Israel's three major broadcasters late Tuesday show an election too close to call.

Millions of Israelis cast their votes to determine their country's next Prime Minister and the makeup of its parliament.

Channel 2 Israel reports the Likud party, headed by Prime Minister Benjamin Netanyahu, has a slight lead over the Zionist Union, led by Isaac Herzog -- 28 seats, over 27 seats. Channels 10 and 1 show the two tied with 27 seats each.

The incumbent claimed victory ahead of a final count.

"Against all odds, we achieved this huge victory," Netanyahu told his cheering supporters. "Now we should form a strong and stable government that will be able to take care of the security, safety and welfare of each and every citizen of Israel."

The Zionist Union responded by saying in a statement that the Likud party "keeps misleading."

"The rightist bloc has shrunk. Everything is possible until the real results are in, when we can know which parties passed the electoral threshold and which government we can form. All the spins and statements are premature," it read.

Official results are not expected to be published until next week, and the process of building coalitions could take much longer.

Gabriel Sassoon, foreign communications adviser for the Herzog campaign, said: "The fat lady has far from sung in this case. We do not know. The parties are neck and neck and it's a matter of coalition negotiations and let me tell you, it's entirely possible to form a center-left coalition at this point. Israel is tired of nine long years of Netanyahu."

Election ballots are for political parties rather than individual candidates. Israel has a proportional representation system, meaning a coalition government is likely to be formed within its 120-seat Knesset.

'Stunning turnaround' for Netanyahu

CNN's Elise Labott described the early results as a "stunning turnaround" for Netanyahu, who took a sharp turn toward the right during the final days of the hotly-contested campaign.

"It seems to have worked. He seems to have energized that right-wing base and now he is neck-and-neck with Isaac Herzog, even inching a little bit ahead of him," she said.

"We'll have to see who's able to form the coalition with the other parties, but it does look as if Prime Minister Netanyahu has fought his way back and has a very good chance of forming this government."

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Before polls closed Tuesday, Netanyahu released a video on his Facebook page urging his supporters to vote, suggesting that leftists are bringing "huge amounts" of Israel's Arab citizens to the polls to vote against his Likud party.

"The right regime is in danger, the Arab voters are coming in huge amounts to the polls," Netanyahu said. "The leftists are bringing them (Arabs) in huge amounts to polls using buses. ... We have an urgent wake-up call."

Arabs make up about 20% of Israel's population. According to the early exit poll estimates, an Arab coalition ranked as the third largest party.

Moshe Kahlon, a former Likud minister who now heads the Kulanu party, said Netanyahu's statement "clearly shows he is feeling the pressure."

"These remarks were inappropriate and regrettable," Kahlon said.

Polls closed at 10 p.m. local time (4 p.m. ET).

Following the release of exit poll estimates, President Reuven Rivlin said that citizens need a ruling government as soon as possible.

"The President will work with all the election bodies to start the consultations process ASAP. We hope to start as soon as Sunday," his office said in a statement.

Netanyahu v. Herzog

Herzog comes from Israeli political royalty. His grandfather, Rabbi Yitzhak HaLevi Herzog, was the first chief rabbi of the state of Israel. His father, Chaim Herzog, was an Army general, an ambassador to the United Nations and the President of Israel.

Before entering politics, Herzog served with a military intelligence unit of the Israeli Defense Forces, rising to the rank of major, and worked as a lawyer and served as the director of the Israel Anti-Drug Authority.

He began his political career in 2003, when he first won a seat in the Knesset with the Labor Party. He held a variety of ministerial positions, including minister of housing and construction, minister of tourism and minister of welfare and social services before becoming leader of the Labor Party in 2013. In those elections, he also became the leader of the opposition, as Netanyahu won another term as Prime Minister.

Herzog has pegged his bid for the premiership on social reform, vowing to "change the nature of the division of wealth." He has also promised to restart stalled peace talks with the Palestinian Authority.

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Netanyahu served for six years in the Israeli Army in an elite commando unit until he was wounded in a rescue operation during an airplane hijacking in 1972.

In 1976, Netanyahu's brother was killed in a raid to try to free hostages in Uganda from an Air France jet hijacked by pro-Palestinian terrorists. Netanyahu set up an anti-terror institute in his name. His outspokenness on the threat of terrorism attracted attention, and he was given high-profile diplomatic assignments.

In 1988, he was elected to the Knesset. In 1996, he became Israel's youngest Prime Minister. He was defeated three years later after signing an interim peace agreement with then-Palestinian leader Yasser Arafat. In 2009, he again became Prime Minister.

CNN's Labott says Netanyahu's emphasis on security -- particularly speaking out loudly on Iran -- and his counteroffensives against Hamas in Gaza have boosted his popularity in Israel.

But Labott says peace with the Palestinians remains elusive, and Netanyahu is finding himself increasingly alienated from Western partners.

As negotiations with Iran near a crucial state, Netanyahu has sided against the White House, telling the U.S. Congress this month that a proposed agreement was "a bad deal" and would not be supported by Israel, which would stand alone if necessary to defend its people.