Washington: US President Barack Obama on Tuesday appeared to have launched his re-election campaign by asking people to vote for him and promising that he would continue to deliver on "big change" in a second term.

"I know that the change we fought for in 2008, we have had to grind it out to make it happen. After all that's been going on in Washington, all the nonsense that takes place here sometimes, it's tempting to believe, well, maybe it's not possible to do everything we wanted," Obama said on Monday.

"I want to remind everybody what I said in the last campaign - real change, big change is hard. It's always been hard. It takes more than a single term. It may take more than a single President," Obama said asking people to vote for his reelection at an election campaign event in Washington.

Acknowledging that the upcoming presidential elections later this year might be harder than the last one, Obama promised his supporters that he will finish the job that he started in 2008.

"This election may be harder than the last one, but I promise you we will finish what we started in 2008. We're going to keep on. We will press forward. We will remind the world once more why the United States of America is the greatest nation on Earth," he said.

Obama is seeking reelection in the November presidential elections.

"You helped me believe in that change. It wasn't just me; it was you. And we knew it wasn't going to be easy. We knew the change we wanted wasn't going to come quickly," he said.

"If you stick with us, if you keep pushing, if we just keep on going through the setbacks, through the tough times, if you keep reaching for a vision of America that I know you still hold in your hearts, then change will continue to come," Obama said amidst applause.

"If you want to end the cynicism and the game-playing and the point-scoring here in Washington, then this is the election to send a message that you refuse to back down, you will not give up. You intend to keep hoping. You intend to keep fighting for the change that we talked about, the change that we believe in," he said.