Voters went to the polls in Spain on Sunday for a snap general election, and 37.4 million Spaniards who have the right to vote have been urged to do so.

Incumbent Prime Minister Pedro Sanchez cast his vote in Madrid shortly after the polls opened, and he urged people to vote, saying that "all I can do is ask the biggest possible mobilization of voters, to give Spain a strong government that can continue to advance."

"What is going to happen here is important for us, but also for Europe and the world," added Sanchez.

People's Party (PP) leader Alberto Nunez Feijoo said, "I have traveled around Spain ... we don't know what the result it, all we hope is that after 11 a.m. Spain can start a new era."

Leader of Vox party Santiago Abascal predicted "a long night," asking for "mobilization to change Spain's political direction."

Sumar leader Yolanda Diaz said, "In our country people couldn't vote for many years and I ask young people, women and workers to all use their right to do so." "We have had to fight for the right to vote in Spain and we have a lot of stake here," Diaz added.

The snap election was called by Sanchez following the Spanish Socialist Workers' Party's (PSOE) poor display in the local elections held at the end of May.

Polls opened at 09:00 local time and will remain open until 20:00.

The election is the first to be held in the middle of the summer holiday season, and this has led to over 2.6 million people requesting a postal vote, with post offices working seven days a week and staying open until 22:00 in order to process the requests.

Meanwhile, the hot weather predicted for Sunday with temperatures expected to reach 36 degrees Celsius in Madrid, has seen leaders appeal for voters to vote early to avoid the worst of the heat.