The Spanish government is moving to block plans by Catalan separatists to re-elect in absentia the former regional president Carles Puigdemont, who is battling extradition from Germany to Spain.

Government spokesman Minister Inigo Mendez de Vigo says a candidate to Catalonia's top job needs to be present in the regional assembly to propose a governing plan.

He said the government has appealed to the Constitutional Court a recent legal reform by the separatists-dominated Catalan assembly that seeks to pave the way for electing an absent candidate.

The court will end Puigdemont's chances to be re-elected simply by accepting the case, as it is expected to.

Separatists need to elect a new regional chief by May 22 or they risk extending Madrid's direct control over the region.