The leader of Spain's Catalonia region has announced that regional elections will be held in September to determine whether a majority of lawmakers favour an independence drive.

Catalan regional leader Artur Mas said on Wednesday elections will be held on September 27 after he failed last year to convince the central government in Madrid to allow the region to hold an independence referendum.

"So one year after I signed this decree the Catalan people will have the possibility to vote for the state of Catalonia and even for an independent state," he told a news conference, speaking in English.

"We will see on that date if there is a social majority in favour of this political process. This is something that the Catalan people have to decide," he added.

Separatists say Catalonia lawmakers could unilaterally declare independence from Spain if they win a majority of supporters in the 135-member regional parliament.

Regional elections were not due in Catalonia, which accounts for one fifth of Spain's economic output, until 2016.

The administration of Spanish Prime Minister Mariano Rajoy insists the country's constitution prohibits Catalonia from breaking away on its own.

Mas defied Madrid and on November 9 went ahead with a symbolic independence referendum organised by volunteers, after the Spanish government used the Constitutional Court to block plans for an official vote.

Some 80 percent of the nearly 2.3 million who voted on November 9 backed secession, but the turnout was little more than 40 percent.

After the poll Mas outlined a new roadmap towards independence, which included a proposal for early regional elections.

His goal is to obtain an absolute majority and a powerful mandate to open independence negotiations with Madrid within 18 months, paving the way for a binding referendum next year.

But Mas has struggled to persuade separatist parties to join his conservative CiU coalition on a joint list.

Under the agreement which Mas reached with Oriol Junqueras - the leader of Catalonia's second-biggest party, the separatist ERC - the two parties will run separate tickets but with a common roadmap toward secession.