Catalonia will hold a referendum on splitting from Spain on 1 October, the head of the region said on Friday, ratcheting up a confrontation with the central government in Madrid which says such a vote is illegal and must not take place.

Previous secessionist challenges in Catalonia - a populous and wealthy region in northeastern Spain which has its own language and Barcelona as its capital - were blocked by Spain's conservative government and the Constitutional Court.

"The question will be: 'Do you want Catalonia to become an independent state in the form of a republic'," Carles Puigdemont, the head of the regional government, said.

He said attempts to agree a date and the wording of the question with the Madrid government - which is vehemently opposed to allowing Catalonia to split from Spain - had failed.