US President Barack Obama got an exceptional spike of more than one million "likes" on Facebook this week in his battle with Republican Mitt Romney in the social media space, a monitoring site showed.

The Inside Facebook website that tracks the social media giant showed Obama gained some 1.1 million "likes" on Tuesday in the largest single-day total for either candidate in a tracking chart that goes back to early September.

Until then, the largest one-day total for either candidate had been 189,000 for Obama last week.

There was no indication from the Obama campaign of any new ad strategy for Facebook, but analysts said there are ways to boost visibility on Facebook through so-called "sponsored" posts, which are paid messages.

"There are a variety of ways to get spikes on Facebook, from contests to really being active to events happening in public," said Alan Rosenblatt, a longtime consultant who follows social media with the Center for American Progress Action Fund.

Rosenblatt said both candidates appear to be using Facebook "quite effectively."

"You can pay relatively small amounts of money to push out your message not just to friends. When you pay for a promoted post you can target your friends, or you can target friends of friends to reach out to new people.

Rosenblatt said some of the likes might have been from supporters in response to Obama's weak debate performance last week or a reaction to the flap over Romney's comments about the furry public television character Big Bird.

Because Obama already has a large presence on Facebook, "he could ... potentially reach millions."

Obama has a far greater social media presence than Romney.

The president has more than 30.6 million "likes" on Facebook, compared to 8.8 million for Romney. Meanwhile, Obama has some 20.7 million Twitter followers to 1.3 million for his opponent. Obama also leads on other social media such as Google+, YouTube and Pinterest.

But technology analyst Charlene Li said the numbers are misleading because "Obama has had four years as candidate and president to gather his followers," and that "what will matter in this election is how engaged these followers are."