US vice president Kamala Harris has picked Minnesota governor Tim Walz to be her running mate in the presidential election, according to three people who spoke to The Associated Press on condition of anonymity.

In choosing Mr Walz, she is turning to a Midwestern governor, military veteran and union supporter who helped enact an ambitious Democratic agenda for his state, including sweeping protections for abortion rights and generous aid to families.

Ms Harris hopes to shore up her campaign’s standing across the upper Midwest, a critical region in presidential politics that often serves as a buffer for Democrats seeking the White House.

The party remains haunted by Republican Donald Trump’s wins in Michigan and Wisconsin in 2016.