Barack Obama and Mitt Romney have taken part in the second US presidential election debate.

With the November 6 election three weeks away, the second of three debates with Republican rival Romney represented one of Obama's final chances to make an impression with voters.

Obama made the most of it with a focused, aggressive effort. It was a sharp departure from his listless first debate two weeks ago, when Romney's dominant performance ignited a resurgence by the Republican that left the race virtually even heading into Tuesday's meeting.

The President made sure to work in all of the attack lines he had neglected in the October 3 debate.

He hammered Romney for the wealthy Republican's low personal income tax rate and Romney's now-infamous dismissal of "47 per cent" of the electorate, as seen in a secretly recorded video of the former Massachusetts governor.

Obama also crisply outlined the accomplishments of his first term in office - from saving the auto industry to killing Osama bin Laden - and framed his answer on a question about women's rights in movingly personal terms.

Romney had his moments as well, especially when describing promises Obama had made and not kept.

The Republican avoided the type of defeat that Obama suffered in the October 3 debate, but the night belonged to the President, according to analysts.