Scotland's voters make their choice in independence referendum

Glasgow, Scotland (CNN) -- Scotland's voters are heading to the polls Thursday to cast their ballots in the country's landmark independence referendum.

There, they will face a straightforward yes/no question: Should Scotland be an independent country?

More than 4.2 million people have registered to vote, the largest electorate ever in Scotland, and turnout in the referendum is expected to be high.

A vote for independence would mean Scotland, with its population of about 5.3 million, splits from the rest of the United Kingdom, made up of England, Wales and Northern Ireland.

Voting can take place from 7 a.m. until 10 p.m. local time (2 a.m. to 5 p.m. ET) at more than 5,500 polling stations across 32 districts nationwide, from the remote highlands and islands to the big cities of Edinburgh and Glasgow.

Voting was brisk at one polling station in Glasgow as the polls opened, with many people voting on the way to work or before taking their children to school.

Results from the different areas will come in overnight into Friday morning local time, with Chief Counting Officer Mary Pitcaithly expected to announce the outcome "around breakfast time."

Bad weather or the sheer volume of votes cast could slow down the counting process. However, the weather forecast appears good so far -- important when some ballot boxes must be collected by helicopter, plane or boat from polling stations on distant islands.

A simple majority is needed for either side to claim victory.

Scotland's First Minister Alex Salmond has led the pro-independence "Yes Scotland" campaign.

The main parties in Westminster, the seat of the UK government, have joined forces behind the pro-union "Better Together" campaign.

For the first time, the vote has been extended to 16- and 17-year-olds living in Scotland. Nearly 110,000 people aged under 18 have registered to vote.

Voters in the referendum do not have to be British citizens; Commonwealth, Irish and EU citizens who live in Scotland and are registered to vote there can cast a ballot. However, Scots living outside Scotland do not have a say.

Nearly 790,000 people applied for a postal vote -- the largest volume of registration for postal votes ever in Scotland.