US Presidential Debate 2012
President Barack Obama answers a question as Republican presidential nominee Mitt Romney listens during the first 2012 US presidential debate in Denver.

Healthcare, taxes and the economy have dominated the first presidential debate between US President Barack Obama and Republican challenger Mitt Romney in Denver.

The 90-minute debate witnessed both the presidential hopefuls highlighting each other's policy flaws on domestic affairs as well as the economy, highlighting the pair's ideological differences ahead of the 6 November election.

Unlike his unimpressive performances in the campaign trails, the well-prepared and poised Romney was on the offensive throughout the debate. Citing figures and statistics, the challenger attacked Obama on America's sluggish economic growth and 8.1 percent unemployment rate.

"Now, I'm concerned that we're on the path that's just been unsuccessful. The president has a view very similar to the one he had when he ran for office four years ago, that spending more, taxing more, regulating more, if you will, trickle-down government would work. That's not the right answer for America," said Romney.

The Republican candidate also attacked Obama's 2010 healthcare law and pledged to scrap it if he becomes the president to reduce the budget deficit. He accused his rival of misrepresenting his tax plans during the campaign trails and said he would not reduce taxes for wealthy Americans.

Obama responded by saying Romney would "double-down" on the economic policies during the period of the Bush administration which the Republicans are still boasting about.

"We ended up moving from surpluses to deficits and it all culminated with the worst recession since the Great Depression," said Obama.

The President also criticised Romney's proposals to overhaul the US tax system by imposing a 20 percent across-the-board tax cut, and maintained it is impossible to make up the resulting cost of nearly $5 trillion simply by closing existing tax loopholes.

"The fact is that if you are lowering the rates the way you described, then it is not possible to come up with enough deductions and loopholes that only affect high-income individuals to avoid either raising the deficit or burdening the middle class. It's math. It's arithmetic," said Obama.

"Virtually everything he said about my tax plan is inaccurate," Romney snapped back.

The two men were seen arguing with debate moderator Jim Lehrer over the allotted time to answer each question.

The debate was the first of three discussions between Obama and Romney scheduled to take place before the presidential election.

According to a CNN/ORC snap poll, 67 percent of registered voters surveyed thought Romney won the debate at the University of Denver, compared with 25 percent for Obama.