Major US media outlets are projecting a win for former US President Donald Trump in five states on Super Tuesday, a critical day in the race to nominate a candidate for the presidential election in November.

Republican primaries and caucuses were held in 15 states. ABC News and others project Trump's win in the states of Virginia, North Carolina, Tennessee, Oklahoma and Maine.

Trump, who is inching towards a comeback, has a big lead over former US ambassador to the United Nations Nikki Haley with nine wins and one loss in the previous nomination races.

Trump leads Haley in average approval ratings in opinion polls by more than 60 points.

Now, attention is on whether Trump will win all 15 states.