Portugal's political parties were preparing Wednesday for a landscape without Antonio Costa, who had been prime minister since 2015 but quit suddenly the day prior when he was implicated in a corruption probe. 

Marcelo Rebelo de Sousa, the conservative president, was due to meet with the heads of the main political parties starting at 1100 GMT Wednesday, before deciding whether to ask a party leader to try to form a new government or to dissolve parliament and call for new elections.  

The main political formations on both the right and the left have said they are prepared to go to the polls.

"The circumstances call for giving a voice to the Portuguese people and organizing anticipated elections," said Luis Montenegro, president of the Social Democratic Party (PSD), the main centre-right opposition party.

On the left, Costa's Socialist Party is ready for all scenarios "whether early elections or a new head of government", said party president Carlos Cesar.

After consulting the parties, the president of the Republic will meet Thursday with the Council of State, an advisory body that includes former presidents, before addressing the nation in the evening to present his decision.    

The prime minister's resignation sent off shock waves in Portugal, with newspaper headlines speaking of the "end of a cycle", "the earthquake of November 7", and a "political bomb." 

"Antonio Costa has entered Portuguese political history as the first acting head of government implicated in a criminal affair," the Publico daily wrote Wednesday. 

- 'Influence peddling' -

Tuesday began with a series of searches in ministries, lawyers' offices, and the residence of the prime minister, before leading several hours later to Costa's surprise resignation. 

He took his decision after learning that his name was cited in an investigation into the approval of a hydrogen plant south of Lisbon and a lithium mine in the north of the country.  

The probe involves suspicions of "misappropriation, active and passive corruption by political figures, and influence peddling", according to prosecutors.  

Costa is himself suspected of intervening "to unblock procedures" in the approval process, and will be the object of a separate investigation, the prosecutors said.  

"In these circumstances, I evidently had to resign," Costa told a press conference Tuesday, insisting he had done nothing illegal.  

After winning an absolute majority in January 2022 -- a rare feat among Europe's leftist parties -- Costa has seen his popularity decline after a series of scandals.   

The departure of the 62-year-old opens a battle for leadership within his Socialist Party.  

The investigation also led to the indictments of Infrastructure Minister Joao Galamba and the arrest of Costa's Chief of Staff Vitor Escaria and his advisor Diogo Lacerda Machado. 

They will be informed of the details of their pre-trial detention later Wednesday.

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