The election took place in the summer holidays and amid intense heat for much of the country.
Spaniards voted in a potentially close-run general election on Sunday that could see Prime Minister Pedro Sanchez's governing Socialists lose power and a far-right party make up part of a new government for the first time in 50 years.
Sanchez called the election early after the left took a drubbing in local elections in May, but his gamble to wrong-foot his opponents could backfire.
Opinion polls show the election will likely produce a win for Alberto Nunez Feijoo's centre-right People's Party, but to form a government it would need to partner with Santiago Abascal's far-right Vox. This would be the first time a far-right party has entered government since Francisco Franco's dictatorship ended in the 1970s.
Voting will close at 8 p.m. (1800 GMT) (9 p.m. in the Canary Islands) when voter surveys conducted via phone calls over the past week will be released. All ballots are expected to be counted by midnight, confirming the party with the most votes.
Both the left and right blocs have the potential to form coalitions, which will need at least 176 seats in the 350-seat lower house of congress. A new parliament must be constituted by Aug. 17, but negotiations between parties to form a government can go on for months.
An analysis of opinion poll data by Spain's El Pais newspaper on July 19 when polling ended projected a 55% chance of a PP/Vox coalition, a 15% chance of Sanchez staying in power with a patchwork leftist coalition and 23% chance of a hung parliament and a repeat election.
As Sanchez went to vote in Madrid he was greeted by one small group of people shouting "liar" and a similar-sized group shouting "prime minister", TVE footage showed. He told reporters he had "good feelings" about the election outcome.
The prime minister's minority government is currently in coalition with far-left Unidas Podemos that is running in Sunday's election under the Sumar platform.
Feijoo said he hoped Spain could begin a "new era".
VOX leader Abascal said "the important thing today is whether Spain changes course" and thanked voters for "disrupting their rest" to cast their ballots, while Sumar leader Yolanda Diaz said "rights are at stake" and urged people to vote in what were "likely the most important elections" for her generation.
The election took place in the summer holidays and amid intense heat for much of the country.
Voter turnout stood at around 40.5% at 2 p.m. (1200 GMT), according to the Interior Ministry, up from 37.9% recorded at the same time during the last election in November 2019.
Postal workers arrived at polling stations with boxes of postal votes, after the postal service reported on Saturday that these had set an all-time record of 2.47 million as people cast their ballots from the beach or mountains.
"The status quo scenario and a hung parliament are still a real possibility, likely with 50% combined odds in our view," Barclays wrote in a recent note to clients, citing the thin margin in PP's favour and overall uncertainty regarding polling and voter turnout.
If a bloc cannot agree on forming a government, new elections must be held - something that has happened twice in the past 10 years.
Such uncertainty could dent Madrid's effectiveness as the current host of the six-month rotating presidency of the European Union Council, as well as its spending of EU COVID recovery funds.
A SWING TO THE RIGHT?
Sanchez's government has passed progressive laws on euthanasia, transgender rights, abortion and animal rights - rights the anti-feminist, family values-focused Vox has said it will seek to repeal if it forms part of the next government.
With the major parties reliant on smaller parties for support, the political centre has been dented.
In Barcelona, engineer Luis Alonso, 43, said "globally the world is heading to being more divided between right and left-wing... here is no different".
In Madrid, Yolanda Fernandez, 67, referred to the Franco era, saying: "I voted for the Socialists because I lived through a period that I don't want to see repeated". She said Vox entering government would mean a "very big setback for social rights".
Sanchez, in office since 2018, has seen his term as prime minister marked by crisis management - from the COVID pandemic and its economic effects to the politically disruptive consequences of the failed 2017 independence bid in Catalonia.
PP leader Feijoo, who has never lost an election in his native Galicia, has sold himself as a safe pair of hands, which could appeal to some voters, experts say.
"I voted for the right, but I won't say whether I voted for the PP or VOX. I think the country needs a change.. Pedro Sanchez is a bad politician," said Juan Carlos Rodriguez, a 63-year-old civil servant voting in Madrid.
An eventual PP government could water down the previous government's green agenda and take a more conservative stance on social issues.
The PP has promised to streamline the tax system, cut taxes for lower-income earners, scrap a recently created wealth tax, boost industry and reduce value-added tax on meat and fish.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)