Outsider Benoit Hamon came first in the French Socialists' presidential primary on Sunday, and will stand against former prime minister Manuel Valls in a January 29 runoff, partial results showed.

With just over one-third of polling stations reporting, Hamon scored 35.21 percent to 31.56 percent for Valls, with former economy minister Arnaud Montebourg eliminated along with four other candidates, party electoral official Thomas Clay announced.