Louisiana on Friday became the first US state to postpone its Democratic presidential primary, citing the rapidly spreading coronavirus threat. "The law provides for extraordinary measures to be taken when facing disasters," Louisiana Secretary of State Kyle Ardoin said. "Today I have certified that a state of emergency exists," he said, postponing the April 4 vote to June 20. The move comes with the battle for the party's presidential nomination still undecided, and just days before Ohio, Florida, Arizona and Illinois -- all of which have reported COVID-19 infections -- hold primaries. Millions were expected to make their choice between former vice president Joe Biden and Senator Bernie Sanders, who are vying for the chance to face Republican President Donald Trump in the November election. The rapidly spreading virus has threatened the Democratic battle with it less than halfway through. Many state and local governments have banned large gatherings, schools -- often used as polling places -- have been closed, and an increasing number of Americans, especially the elderly, are remaining at home. Ohio declared a state emergency last week, but -- with so far only five confirmed COVID-19 cases -- has not put off its primary. Louisiana's move also postpones its Republican primary to June 20, but Trump is the only viable candidate on the ballot and so his winning the party's choice seems inevitable. So far, Biden leads the Democratic race, with 878 delegates over Sanders' 725. To win the nomination, a candidate needs a majority of 1,991. pmh/to