Mitt Romney's running mate Paul Ryan will break off the campaign trail next week for three days of debate preparation ahead of his face-off with US Vice President Joe Biden, a campaign aide said.

Ryan will hunker down for "three days in Virginia for debate prep," campaign aide Brendan Buck told AFP on Saturday, as Romney and President Barack Obama both dropped off the campaign trail ahead of their own first debate October 3 in Denver, Colorado.

The presidential contenders engage in three nationally televised debates, while Biden and Ryan have just one shot against each other, an October 11 showdown at Centre College in Danville, Kentucky.

Ryan, 42, is a novice on the wider political stage compared to Biden, who has engaged in several nationally televised debates with rivals such as Republican vice presidential candidate Sarah Palin in 2008 and Democrats vying for the party's presidential nomination that year.

But Ryan is a number-crunching budget expert with substantial command of financial data, and his supporters have long labeled Biden as gaffe-prone and too liberal for many American voters.

Biden, a Romney aide told The Washington Post, "has been the president's strongest surrogate throughout the past four years, and the biggest Achilles' heel he'll have is the president's record."

For his part, Romney withdrew to Vermont for debate camp in early September, and is expected to gather with aides and fellow Republicans again in the coming days for final debate preparations.

Obama travels to Nevada for an event on Sunday, and spends the next two days in the town of Henderson ahead of Wednesday's debate, according to the White House.

On Monday, Ryan will embark on a two-day "Real Recovery Bus Tour" across the political battleground state of Iowa, his campaign said, before he heads to Virginia.