The first openly gay US presidential candidate, Pete Buttigieg, has dropped out of the Democratic race after a resounding defeat in the South Carolina primary.

Among a crowded field of moderate Democratic candidates, Buttigieg said it would be irresponsible to stay in the race any longer.

His decision comes before the biggest day of primary voting tomorrow - Super Tuesday - in which 14 states head to the polls.

USSC chief executive Simon Jackman provided comments for this report on ABC's PM.