The Democratic Party Super Tuesday winners, state by state

Former vice president Joe Biden scored a string of wins over leftist Bernie Sanders in the Super Tuesday contests to pick the Democratic challenger to President Donald Trump this November.

Among the 14 states at play, US networks have so far projected nine wins for the centrist Biden, with his strong showing in the country's south demonstrating the depth of his support among African Americans.

Biden claimed the second biggest prize of the night in Texas though the very biggest was yet to come: delegate-rich California, where the self-described socialist Sanders is strong favourite.

Both California and Maine were still considered too close to call.

Sanders has three victories so far: his home state of Vermont, and Colorado and Utah in the west. He has lost in Minnesota and Oklahoma, where he handily defeated Hillary Clinton in 2016.

A total of 1,357 delegates are at stake on Tuesday, about a third of the overall national total.

Biden, who has the backing of his party's establishment, also appeared to have profited from the endorsements of former centrist rivals including Amy Klobuchar and Pete Buttigieg, who dropped out in the run-up to the races.