Democratic US presidential candidate Hillary Clinton and US Senator Tim Kaine (D-VA) wave to the crowd during a campaign rally at Ernst Community Cultural Center in Annandale, Virginia, US, July 14, 2016. [Photo/Agencies]

WASHINGTON - Hillary Clinton named US Senator Tim Kaine as her running mate on Friday, making a safe choice that will help her present the Democratic ticket as a steady alternative to the unpredictable campaign of Republican presidential rival Donald Trump.

The selection of Kaine, a self-described "boring" Virginian with wide governing experience and a reputation for low-key competence, could appeal to independents and moderates but could also anger liberal groups that object to his advocacy for an Asian free-trade pact.

But the Spanish-speaking former Virginia governor and Richmond mayor fits Clinton's long-stated criteria that the vice presidential choice be a capable partner who is ready to take over the presidency if necessary.

Clinton made the announcement via Twitter and a text message to supporters after the first day of a two-day campaign swing in Florida. She called Kaine to tell him about 40 minutes before the announcement, and called President Barack Obama shortly after Kaine.

"I'm thrilled to tell you this first: I've chosen Sen. Tim Kaine as my running mate. Welcome him to my team," she said in her text message.

Kaine, 58, edged out two other finalists - Cory Booker, a US senator from New Jersey, and Agriculture Secretary Tom Vilsack, according to a Democratic source familiar with the discussions.

Clinton also bypassed candidates who would have generated more excitement among liberal and Hispanic activists, including progressive favorite US Senator Elizabeth Warren and two Hispanic members of Obama's Cabinet, Julian Castro and Thomas Perez.