WASHINGTON - US Republican presidential candidate Mitt Romney has picked Wisconsin Rep. Paul Ryan as his vice presidential running mate, US media reported Friday, citing Republican sources.

A formal announcement would be made at 9 am (1300 GMT) Saturday in Norfolk, Virginia, during a public event aboard the renowned USS Wisconsin, a decommissioned World War II-era warship.

NBC, CNN, AP and several other US media outlets reported that Ryan is Romney's choice for running mate, citing Republican and Romney campaign officials.

The announcement comes at a time as the candidate is starting this weekend a bus campaign tour, dubbed "The Romney Plan For A Stronger Middle Class." The bus would travel through Virginia, North Carolina, Florida and Ohio, over the weekend through Monday.

During the trip, Romney will stump with Virginia Gov. Bob McDonnell, Florida Sen. Marco Rubio and Ohio Sen. Rob Portman.

Romney's upcoming announcement was anticipated as he is believed to do it before the Republican National Convention, which is to be held by the end of the month. His campaign plans to use the announcement to boost his fund-raising and poll ratings and get at least one week of positive press coverage.

Wisconsin Representative Paul Ryan listens during a campaign event at Monterey Mills in Janesville, Wisconsin, in this June 18, 2012 file photo. [Photo/Agencies]