Madrid,  A new regional parliament will be elected in the Spanish capital, Madrid, on Tuesday, with the right-wing populist Vox party hoping to form part of the government.

The vote is therefore being seen as having nationwide significance beyond the economically strong region, dpa news agency reported.

According to opinion polls, the conservative People's Party with the incumbent regional President Isabel Diaz Ayuso could double its share of the vote compared to the last election to about 40 per cent.

To form a government, however, Ayuso may have to rely on Vox, a prospect she has described as unproblematic.

The possible coalition has united the otherwise divided left, which has called for a massive turnout during a bitter election campaign.

Spain's Socialist Prime Minister Pedro Sanchez has warned that a People's Party pact with Vox could endanger the democratic system of the whole of Spain.

The left-wing Unidas Podemos, which is in coalition with Sanchez at the national level, even issued the slogan, "Fascism or democracy".