The PSOE received 28.1% of votes, which would land them 116-121 of the 350 seats in parliament, according to a telephone poll carried out by GAD3 on behalf of Spanish national broadcaster RTVE.
Incumbent Prime Minister Pedro Sanchez, a member of PSOE, would once again need the support of left-wing Podemos and Catalan pro-independence parties in order to form a government.
The poll predicts 69-73 seats for the conservative People’s Party (PP), 48-49 seats for center-right Ciudadanos, 42-45 for Podemos and 36-38 for far-right party Vox.
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It would be the first time that a far-right party has had such electoral success in Spain since 1982.
While no exit polls were conducted, RTVE commissioned a telephone poll involving 12,000 interviews to get an early idea of results.
At 73.37%, voter turnout was the third-highest in the history of Spanish democracy after the 1996 elections (77.38%) and the 1993 elections (76.4%), according to official figures.
Source: Far-right surges in Spain
