Spain's governing Socialists won the country's third election in four years, but have fallen short of a majority.
PM Pedro Sánchez's party polled 29% and will need the help of either left-wing Podemos and regional parties, or the centre right, to form a government.
For the first time since military rule ended in the 1970s, a far-right party is set to enter parliament.
Vox opposes multiculturalism, unrestricted migration, and what it calls "radical feminism".
The other big story of the election was the collapse in support for the Popular Party (PP), which governed Spain until it was dumped from power in May 2018 in a no-confidence vote.