The five leading candidates running for Spain's Prime Minister voted on Sunday's morning and encouraged Spaniards to leave home for the polling stations.

Spain's current prime minister and favorite in the polls, the socialist Pedro Sanchez, voted around 9:30 a.m. local time (0730 GTM) in Pozuelo de Alarcon, just outside Madrid.

The socialist candidate asked Spaniards to go to the polls and exercise their right to vote.

"I hope that Spaniards send a clear message that there is a sufficient parliamentary majority to rule the country. I would like to express my desire to hold an election day that means an open doors day towards the future," Sanchez told press after voting.

Later, in the Madrid neighborhood of Vallecas, Pablo Iglesias, the leader of the left party Unidas Podemos, asked citizens to respect the results.

"My feeling is that there is a large progressive majority in Spain, but today we have to respect that Spaniards vote in freedom," he said.

The candidate of the Liberal party Ciudadanos, Albert Rivera, voted in the Catalan town of L'Hospitalet de Llobregat, northeast Spain, and called on Spanish society to mobilize.

"I ask Spaniards to go and vote for a Spain that looks forward," Rivera said in a speech to the media.

The leader of the far-right VOX party, Santiago Abascal, who is predicted by the polls to be the great advent of the election, also asked people to respect the results of the vote.

"Millions of Spaniards are going to vote without fear, defend democracy, the nation and coexistence among citizens," Abascal stressed.

The last candidate to cast his vote was Pablo Casado, from the Popular Party (PP, center right). He went to a polling station in a school located in Madrid's neighborhood of Salamanca (center) and highlighted the importance of the day.

"We face the most decisive elections for the destiny of Spain in recent times, which is why I think we should all vote united and together," Casado said.

More than 36 million Spaniards are called to cast their vote on Sunday's election, which is marked by uncertainty, since no survey clearly predicted who would be the next prime minister.

At 20:00 p.m. local time (1800 GTM) the first results will be revealed and the Interior Ministry will unveil the first provisional official data at 22:30 p.m. local time (2030 GTM).