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.
Opinion polls in recent weeks have unanimously predicted the new ballot today 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.
Recent polls have suggested the conservative Popular Party would win most votes but would 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.
