The UK will go to the polls on Thursday for the country's third general election in less than five years, ONA reports citing BBC.
The contest, the first to be held in December in nearly 100 years, follows those in 2015 and 2017.
Polling stations in 650 constituencies across England, Wales, Scotland and Northern Ireland open at 07:00 GMT.
After the polls close at 22:00 GMT, counting will begin straight away. Most results are due to be announced in the early hours of Friday morning.
A total of 650 MPs will be chosen under the first-past-the-post system used for general elections, in which the candidate who secures the most votes in each individual constituency is elected.
In 2017, Newcastle Central was the first constituency to declare, announcing its result about an hour after polls closed.
Elections in the UK traditionally take place every four or five years. But, in October, MPs voted for the second snap poll in as many years. It is the first winter election since 1974 and the first to take place in December since 1923.
Anyone aged 18 or over is eligible to vote, as long as they are a British citizen or qualifying citizen of the Commonwealth or Republic of Ireland and have registered to vote. Registration closed on 26 November.