MADRID (AP) - A strong showing by a pair of upstart parties in Spain's general election on Sunday is threatening to upend the country's traditional two-party system, with an exit poll projecting that the ruling Popular Party won the most votes but fell far short of a parliamentary majority.

MADRID (AP) A strong showing by a pair of upstart parties in Spain's general election on Sunday is threatening to upend the country's traditional two-party system, with an exit poll projecting that the ruling Popular Party won the most votes but fell far short of a parliamentary majority.

The exit poll for the state-owned RTVE channel gave the Popular Party 26.8 percent of the vote. The main opposition Socialist Party, with 20.5 percent was running neck-and-neck for second place with new far left party Podemos, with 21.7 percent, the poll said.

It put support for the new business-friendly Ciudadanos party far behind the others, at 15.2 percent. Jorge Clemente, spokesman for pollster TNS Demoscopia, says its figures are based on 180,000 face-to-face interviews.

Spain has been dominated for more than three decades by the Popular Party and the Socialists, which have alternated running the government.

The country could end up with a host of coalition government possibilities. The most likely ally for the Popular Party is Ciudadanos, while the center-left Socialists would probably team up with Podemos. There's also the possibility of a three-way alliance between the Socialists, Ciudadanos and Podemos.

Days or weeks of negotiations may be needed to determine the outcome which will be unprecedented because the Socialists and the Popular Party have previously only needed support from tiny Spanish parties to get a majority in parliament when they didn't win one from voters.

Podemos and Ciudadanos both gained strength by portraying the Popular Party and the Socialists as out-of-touch behemoths run by politicians who care more about maintaining their own power than citizens' needs.

Miguel Redondo, a 19-year-old Madrid university student, voted for Podemos because "it's the party that best understands the difficulties that young people are going through" in a nation where joblessness for people under 25 is more than double the country's overall 21 percent unemployment rate.

Spain's 36.5 million registered voters were electing representatives to the 350-seat lower house of parliament and to the Senate, which has less legislative power. Voting was brisk with lines outside some polling station and voter participation of 58.4 percent by 6 p.m. (1700 GMT, 12 p.m. EST), up slightly compared to the 2011 election.

Prime Minister Mariano Rajoy has said he would seek an alliance to prevent a leftist coalition from taking power as one did in neighboring Portugal last month.

Francisco Herrera, a 43-year-old porter in Madrid, said he was disappointed with Rajoy's leadership, but would vote for his Popular Party because it "defends the economy and the type of government that suits us right now."

The nation's devastating economic crisis, non-stop corruption scandals and a separatist drive in the northeastern region of Catalonia have dominated Spanish politics over the past four years. Rajoy has boasted about his handling of the economy, done his best to skirt the corruption minefield and has vowed to halt the independence push.

His administration's biggest success has been in pulling Spain back from an economic abyss in 2012 and returning the economy to steady growth, but the jobless rate has come down slowly and salaries for people entering the workforce are 30 percent lower than they were in 2008. This has fueled claims by Ciudadanos and Podemos that the Socialists plunged Spain into an economic crisis and the Popular Party has failed to fix the problem.

Rajoy's party also adopted unpopular austerity measures and labor and financial reforms that are credited with creating jobs but damaging the country's social welfare system. Although Spain's economy is now one of the fastest-growing in the 28-nation European Union, its unemployment rate is the second-highest in the EU after Greece.

His administration has been hurt by his U-turn on a promise not to raise taxes and by cuts to national health care and public education. Many Spaniards are also angry about what they perceive as the impunity of politicians and business leaders amid incessant corruption cases.

The question of independence for economically and politically powerful Catalonia has divided that region and soured political ties with the rest of Spain. Rajoy vows to quash what is seen as the biggest threat to Spanish unity in recent decades. Other parties favor negotiations to devolve more power to Catalonia.

Rajoy, 60, champions conservative social policies, siding with the Roman Catholic Church against abortion. He has raised questions about his future as the Popular Party leader, however, by including his deputy, 44-year-old Soraya Saenz de Santamaria, on campaign posters.

Pedro Sanchez, a 43-year-old former university economics professor, was unknown to most Spaniards until he was elected leader last year of the Socialists.

Political science professor Pablo Iglesias, a ponytailed 37-year-old, and his radical left Podemos party want to break the mold of Spanish politics. Podemos was born from massive Madrid street protests in 2011 that drew mainly young Spaniards weary of corruption.

Ciudadanos has the media-savvy Albert Rivera as its leader. At 36, he is the youngest candidate, and his moderate, business-friendly policies plus a pledge to crack down on corruption have attracted voters.

After casting his ballot in a Barcelona suburb, Rivera said the election marks the start of a new era especially for young Spaniards like him born after the nation's 1939-1975 dictatorship.

"For the first time, those of us who didn't experience the first democratic transition are experiencing a second one," Rivera said.

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Associated Press writer Cristina Fuentes-Cantillana contributed to this report.