Jon Ossoff, the Democrat candidate, came agonisingly close to pulling off an election victory in a safe Republican seat in Georgia on Tuesday night that would have sent shockwaves through Donald Trump's party.

Nevertheless, the 30-year-old, claimed a "victory for the ages" and will now head into a June run-off with Republican Karen Handel holding all the momentum.

The strong showing will give Democrats hope as they attempt to rebuild ahead of next year's Midterms and Mr Ossoff said Tuesday's result had "shattered expectations".

"No matter what the outcome is tonight, whether we take it all or whether we fight on, we have defied the odds. We have shattered expectations. We are changing the world," he told his cheering supporters.

"Your voices are going to ring out across this state and across this country."

Mr Ossoff won more than 48 per cent of the vote, according to several projections early on Wednesday, in a crowded field of 18 candidates, including 11 Republicans. It was just shy of the 50 per cent he needed to win the Georgia 6th congressional district seat outright.