More on KentOnline
More on KentOnline
It's said to be the most important by-election of the last 30 years with repercussions likely to be felt far beyond the borders of Kent.
Since the defection of Mark Reckless from the Conservatives to Ukip, the constituency has been inundated with leaflets, ministerial visits and speculation.
Now, with the ballot boxes open, residents could be on the brink of creating political history.
National media pundits predict a Ukip win - which would give the party its second MP - could spark a Conservative leadership challenge.
Voting at Hoo Village Hall, resident Dave Middleton said: "I think Ukip are going to get in because everyone wants to make a protest. I think everybody is fed up with the normal parties.
"Farage sticks to his guns, he's open and honest. They've got some very good policies and they've got some that aren't so good."
The latest Lord Ashcroft poll puts Ukip 12 points ahead of the Conservatives, who are in turn 15 points ahead of Labour.
The picture is very different to the results in 2010.
Mark Kelly was a Cuxton polling station and voted Ukip having always previously voted Labour.
He said: ""I'm a Trade Unionist as well but this year I just thought 'no'. I will not be dictated to by Europe, and I have concerns over immigration.
"I think it will be closer between UKIP and Conservatives that people initially thought."
The KM Group's political editor Paul Francis said: "There is no doubt that the result of this by-election will have repercussions for all parties and the potential to change the political landscape in Kent and beyond.
"It's been described as the most important by-election in 30 years and that is not an exaggeration."
There are 79,163 people registered to vote in the constituency, with 50 polling stations dotted around the area, open from 7am.
The result is expected about 3.30am on Friday, with High Sheriff of Kent, Hugo Fenwick, acting as Returning Officer.
Some voters said they will be glad when it is all over.
Michael Gear, 74, who was voting at 9am this morning, said: "The intensity of the parties in this election has been ridiculous.
"I've been inundated with phone calls and letters through the post. How much money it's cost them God only knows, but it's a total waste of money.
How KentOnline has followed the campaign trail
"Having the Prime Minister visiting five times has made absolutely no difference - or any other ministerial visits for that matter."
After the electorate decides, we will be bringing you all the latest by-election news as it happens.
During the night we will be:
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