The leader of Spain's far-left Unidas Podemos party said that, on the basis of results in Sunday's national election, he would be open to forming a left-wing coalition government with outgoing Prime Minister Pedro Sanchez's Socialists.

"I have expressed to him (Sanchez)...our willingness to work towards a coalition government," Pablo Iglesias told supporters in Madrid after a tally of results with more than 95 percent of votes counted showed Podemos winning 42 seats.

The two parties combined would be around 11 seats short of a parliamentary majority, the same interior ministry tally showed.

Forming such a coalition "will take much time and I would ask for your patience," Iglesias added.