The Spanish region of Catalonia has voted in a referendum on independence.

We answer key questions of the October 1 vote below, but for a more in-depth explainer please see here.

What's the question?

"Do you want Catalonia to become an independent state in the form of a republic?"

Who can vote?

Only Catalan residents of voting age, 18 and above, are entitled to participate in the referendum. An estimated 5.3 million of the region's 7.5 million population are eligible to vote.

Up to 85 percent are in favour of holding the referendum, according to a poll conducted by El Periodico de Catalunya, a regional daily newspaper.

However, only about 41 percent said they intend to vote "Yes" to independence when asked in June of this year by the Centre for Opinion Studies, the regional government's polling body.

A number of pro-union Catalans are expected to boycott the vote, on the grounds that the referendum is illegal.

How can Catalans vote?

The Spanish government has sealed off a number of polling stations in Catalonia in order to prevent voters from taking part in the referendum.

Up to 1,300 of 2,315 designated voting stations have been reportedly closed by Spanish police, who have been mobilised in the thousands, according to the central government in Madrid.

In response, the Catalan government has said voters may use any polling station to cast a ballot if their designated voting place was shut.

A number of clashes between security forces and would-be voters have already broken out across the region.

When is a result expected to be announced?

Voting was scheduled to begin at 09:00 local time (07:00 GMT), with the ballots expected to close 11 hours later at 20:00 local time (18:00 GMT).

The result of the referendum is expected within 48 hours.

Catalonia government's electoral commission is responsible for overseeing the vote and the counting.

Why does it matter? What happens next?

Catalan's regional government claims it will declare independence within 48 hours if there is a majority "Yes" vote in favour of independence.

Such an outcome would have major consequences for the Spanish central government.

Prime Minister Mariano Rajoy's centre-right administration has reacted strongly to the planned vote, attempting to prevent the referendum, which it deems to be illegal on the grounds that Spain's 1978 constitution grants the national government exclusive power to hold referendums.

If Catalonia were to declare unilateral independence following the referendum, the Spanish government could suspend Catalan autonomy, plunging the nation into a political, and constitutional crisis.

Should a vote against independence be returned, it is likely a new round of Catalan regional elections will follow.

The "referendum bill" was passed by the 135-member Catalan parliament on September 6 with 72 votes in favour and 11 abstentions.