Last night's American election has been the subject of more tweets than any other event in US political history, with more than 20 million election-related messages inundating the social networking site.

"With 20 million tweets, Election Day just became the most tweeted about event in US political history," said Twitter when the record was broken.

After Mitt Romney conceded at around 5.30am GMT, Obama used Twitter to proclaim his own victory and plans for his second term as president.

Obama tweeted "Four more years" along with a picture of himself hugging his wife, Michelle. It was retweeted over 300,000 times within 40 minutes. The number of retweets is still ticking ahead.

The re-election also becomes the most tweeted moment of all time, according to Twitter's official account '@gov.' More than 327,000 tweets were recorded in a single minute when the election results were announced.

Voting topics like Obama, Elections, Romney, and Ohio have been constantly trending on the social networking site.

Both Romney and Obama's campaign team have used the social networking media extensively in seeking votes over recent months.

British Prime Minister David Cameron also took to twitter soon after the results to congratulate "his friend" and said he "looks forward to continue working together."