Exit polls suggest pro-independence parties are likely to win most seats in Cataluña's regional parliament.
But a pro-union party is likely to be the biggest single group.
The latest turn out figures show more than 68% of voters had a say.
An election was called after a disputed poll on breaking away was rejected by Spain.
The Spanish government is hoping the election will help resolve the political crisis that has rocked the region.
The snap poll comes amid a bitter deadlock over the region's drive for independence from Spain.
Voting got underway at 9.00am local time (8.00am Irish time), and closed at 8.00pm Thursday evening.
According to The Local, long queues formed outside some of the region's 2,680 polling stations this morning.
Catalonia's political crisis was sparked by an independence referendum in October, which Spanish officials declared illegal.
Following the contested referendum, the regional Catalan government - led by the then regional president Carles Puigdemont - declared independence from Spain.
The Spanish government, meanwhile, refused to recognise the independence declaration, and instead invoked Article 155 of the country's constitution - allowing it to impose direct rule over Catalonia.
In a tweet earlier today, Mr Puigdemont - who remains in Belgium after leaving Catalonia in late October over fears of being arrested - told voters: "Today is a very important day: not just for today's Catalonia, but for the Catalonia of the future."
Avui és un dia molt important, no per la Catalunya d'avui sinó per la #Catalunya del futur. I tu Laura representes aquesta albada d'esperança. És el moment que la República dels ciutadans jubili la monarquia del 155 #JuntsxCat #21D pic.twitter.com/5v9Meq0qJE
— Carles Puigdemont ðŸŽ— (@KRLS) December 21, 2017