As the race for the White House got underway on Tuesday (November 6), it wasn't just polling booths across the U.S. that saw a huge amount of traffic.

The online Twittersphere was also reaching fever pitch, with celebrities urging their fans to vote.

Katy Perry and Eva Longoria both posted messages in favour of Barack Obama. Perry tweeted a photo of her with the U.S. president and her grandmother with the caption:

"May I exclusively present what might be the cutest photo ever taken. Me, Gma & POTUS!" - the President of the United States.

Longoria, an avid Obama campaigner, added the message, "I Voted" to her profile picture.

Mariah Carey also tweeted out photos of her voting and rapper Chris Brown simply told his Twitter followers to go and "Vote".

'Justin Bieber also contributed to Tuesday's hottest Twitter topic, although the 18-year-old can't vote himself. He's Canadian.

While most tweets seemed to favour Obama, entrepreneur Donald Trump sent out a series of messages backing Republican Mitt Romney.

Tuesday's election has become the most tweeted event in U.S. political history, with more than 31 million tweets sent throughout the day.

At its height, some 327,000 tweets were sent every minute and Obama's winning tweet, which he posted moments before his victory speech in Chicago has become the most retweeted message of all time.