Voters in Catalonia are participating in an election that could propel the northeastern region toward independence from the rest of Spain or quell secessionism for years.

Secessionists have long sought an independence referendum, but Spain's central government has not allowed one, arguing it would be unconstitutional because only it can call such a vote.

Sunday's election is for Catalonia's 135-member Parliament, located in the region's capital Barcelona. Secessionists argue if they win 68 seats, the result would give them a democratic mandate to initiate a split from Spain that could include a unilateral declaration of independence.

The central government of Prime Minister Mariano Rajoy says it will use all legal means to prevent Catalonia from breaking away, an exit European leaders warn would include ejection from the European Union.