Spain's government is fighting off a two-pronged assault from new protest parties after it collapsed in a key regional election ahead of this year's national polls.

The vote in the poor southern Andalusia region was a key test for surging left-wing party Podemos, which hopes to emulate its Greek ally Syriza and win power nationally by campaigning against crisis austerity measures.

But it also saw the entry into the political arena of another party that is helping to transform Spain's political landscape -- the centre-right Ciudadanos.

The main opposition Socialists won the contest overall with 35.4 percent of the vote, keeping control of the region they have governed since 1982 -- but the results were marked by the performance of the other three contenders.

Spain's governing Popular Party (PP) lost 17 seats in the regional assembly with 26.7 percent of the vote, while Podemos and Ciudadanos won their first parliamentary seats on Spanish soil. They won 14.8 and 9.2 percent of the vote respectively.

"The PP is the one with a very serious problem. This could be the beginning of a debacle," said Fernando Alvarez, a professor of constitutional law at Seville University.

Centre-right daily El Mundo called it a "fiasco" for the PP of Prime Minister Mariano Rajoy, summing up the view of most of the Spanish press.

Foreign Minister Jose Manuel Garcia Margallo said the results in Andalusia were "infinitely worse than expected".

- Lesson in humility -

Rajoy had campaigned hard in person in Andalusia in the first electoral clash of a year that will see local and regional polls in May and a general election around November. Catalonia will also hold a regional vote in September, focused on demands for independence.

Rajoy touted Spain's gradual recovery from several years of recession -- but that line apparently did not work in Andalusia, a region which still has an unemployment rate of 34 percent.

"We take on board these results with great humility," said one of the PP's spokesmen, Pablo Casado. "Governing always takes it toll."

The Socialists' triumphant leader Susana Diaz said it was "a lesson for all the political parties".

Podemos's lead candidate in Andalusia, Teresa Rodriguez, said the party was profiting from a "general loss of trust in the two-party forces".

- Ride the 'tsunami' -

Podemos erupted into Spanish politics last May when it won seats in the European Parliament just four months after its founding.

It was initially boosted by Syriza's election victory in Greece in January, but has been given pause for thought by the ongoing squabbles between the Greek party and European powers over the country's crippling debt.

Podemos won less votes than it had hoped, but political scientist Jose Fernandez-Albertos of Spain's state research institute CSIC said its achievement in Andalusia was still "not at all bad".

"If a year ago someone had said that today a party called Podemos would win 15 percent of the vote and another called Ciudadanos would win nine percent, that would have sounded mad, an enormous tsunami," he said.

Analysts said Ciudadanos likely poached some votes from the PP as well as from more moderate protest voters that might otherwise have gone to Podemos.

Ciudadanos was founded in 2006 as an anti-independence party in the Catalonia region but has expanded nationwide in recent months, shaking up a political world dominated for decades by the Socialists and PP.

"There were many disillusioned PP voters, fed up with the government's policies, austerity and the crisis, but previously they had no alternatives," said Fernandez-Albertos.

"That gave the PP a safety net. But now it has disappeared," with the emergence of Ciudadanos, he said.