Spaniards are voting in an unprecedented repeat election that aims to break six months of political deadlock after a December ballot left the country without an elected government.
But opinion polls in recent weeks have unanimously predicted the new ballot will also fail to deliver enough votes for any one party to take power alone.
That would likely consign Spain to another period of protracted political negotiations — and, possibly, another ballot if there is no breakthrough.
Polls suggest the conservative Popular Party will win most votes but will again fall short of a parliamentary majority.
Political negotiations could be complicated by increased support for a new far-left alliance called Unidos Podemos (United We Can), which is expected to finish second.
Election Popular Party leader Mariano Rajoy is hoping to be re-elected as prime minister.
According to the Spanish Constitution, a government must win a vote of confidence in parliament with more than 50 per cent of the possible 350 votes before taking office. If it misses that target, in a second vote 48 hours later it must get 50 per cent of only the votes that are cast — a lower bar which allows parties to abstain from the vote and let a party into power in return for concessions.
If Unidos Podemos, which includes radical leftist party Podemos and the Communist Party, finishes second it would push the moderate, centre-left Socialist Party, which has traditionally alternated in power with the Popular Party, into third place and the business-friendly Ciudadanos (Citizens) into fourth.
The election in Spain comes four days after Britain voted to leave the EU, but Antonio Barroso, a London-based analyst with the Teneo Intelligence political risk consultancy, said it is “unlikely” that decision will have much of an influence on the Spanish election.
“Nevertheless, the ongoing market turmoil fits well with the campaign message of... Rajoy, who has framed the election as a choice between economic stability and a radical left-wing government potentially led by Podemos and its allies,” he said.
Polls opened at 9am local time and will close at 8pm for Spain’s roughly 36.5 million voters. Exit polls with projections of the result are expected within minutes of polls closing, and most votes are expected to be counted by 11pm.
Public anger at high unemployment, cuts in government spending on cherished public services such as welfare and education, and unrelenting political corruption scandals have shaped the two-week election campaign.
After the December election, Mr Rajoy could not get enough support from rival parties to form either a minority government or a coalition.
The negotiations between parties dragged on for months as Pedro Sanchez, leader of the second-placed Socialists, also failed to clinch a deal that would let him govern.
Spain has never had a coalition government.
Pablo Iglesias, the radical college professor leader of Unidos Podemos, has repeatedly said he wants a pact with the Socialists in order to oust Mr Rajoy. But a major sticking point for such a deal is Mr Iglesias’s insistence on letting the powerful north-eastern region of Catalonia stage an independence referendum — a possibility rejected outright by all the other main parties.
Ciudadanos is willing to talk to both the PP and the Socialists but want no deals with Unidos Podemos.
Besides tension over Catalonia, Spanish political debate has been dominated by an unemployment rate that has stood at more than 20% for nearly seven years and is the second highest in the EU after Greece, and an unrelenting stream of corruption scandals, mostly involving the Popular Party and the Socialists.
Reuters