Voting is drawing to a close in one of the UK's most unpredictable general elections in recent history.
After six weeks of campaigning and debate, millions of people have been casting their votes at about 50,000 polling stations across England, Scotland, Wales and Northern Ireland.
Voters are electing 650 Westminster MPs and in England are also voting for more than 9000 council seats across 279 English local authorities.
With opinion polls consistently putting the two main parties - Conservative and Labour - neck and neck, the likeliest outcome is a coalition or minority government.
That magnifies the importance of the unprecedented rise of smaller parties - the UK Independence Party (UKIP), the Greens, Plaid Cymru and, above all, the Scottish Nationalists (SNP).
Some polls have suggested SNP could completely wipe Labour from the map in Scotland, even though 41 of the 59 seats there have previously been Labour heartlands.
A commentator, Tony Travers of the London School of Economics, told the ABC it seemed Scottish voters were flexing their muscles.
"It was almost as if people said, we're now going to show that we want Scotland to have a more powerful voice in Westminster politics - as well as getting any additional powers and tax freedoms that the UK government is going to make available," he said.
"Frankly, nobody - I suspect including the SNP - had predicted [it]."
Some voters are using a vote-swap website to agree to vote tactically for one another in their respective electorates - making their votes more effective.
Huw Jordan is a co-founder of Vote Swap, a website which encourages Green and Labour supporters to exchange votes in tactical arrangements for finely-balanced seats.
"In a constituency like let's say Hampstead and Kilburn in London, where I think the result was down to 40 people in the last election, the difference between a Labour and a Tory [Conservative]," he said.
"So if a large number of Green people vote for Labour in that seat and swap their votes for someone else to vote Green elsewhere, that can actually make the difference in somebody's constituency."
Mr Jordan, in London, said the voting agreements relied on people being honest, because there was no way to check how each vote was cast.
The polls close today at 9am NZST.