Results indicate incumbent president is on course for election victory over divided opposition in October vote.
Argentine President Cristina Fernandez de Kirchner has seen her re-election campaign boosted after she won half the votes against a divided opposition in a presidential primary.
Three of the nine other candidates were battling for second place in Argentina's first-ever open and simultaneous presidential primary on Sunday.
The idea of the open, simultaneous and obligatory primary was meant to force parties to allow voters to choose candidates for president and vice president.
Instead, all the parties simply proclaimed their candidates months ago.
That turned the primary into a kind of nationwide political survey, since voting is mandatory in Argentina and voters could choose any candidate in the primary irrespective of party.
Kirchner had 50 per cent of the votes, when just over half of the ballots had been counted, nearly 38 points ahead of Ricardo Alfonsin, the next closest contender, who had 12 per cent.
Eduardo Duhalde, the former president, got 12 per cent and Hermes Binner, the Socialist Santa Fe Governor, won 10 per cent.
The results suggest that unless the opposition unites around a single candidate, Kirchner has a very good chance of winning re-election.But she faces major challenges, including taming inflation estimated at over 25 per cent without hurting growth and cutting spending in the major grains producer. She will also need to find a way to repay debt without draining central bank reserves.
"I voted for Cristina because I see my children's progress. They all have jobs, homes, cars. We used to travel by donkey," said Aida Peralta, 81, as she celebrated to the sound of drumming outside the president's campaign headquarters.
Cheering supporters waved flags and images of Nestor Kirchner, her late husband and presidential predecessor.
'Big picture'
Many Argentines credit Kirchner, 58, and her late husband with reviving the economy after a crippling 2001/02 financial crisis, when Argentina declared a record sovereign debt default that made it a market pariah.
"I call on everyone to think about the big picture, to be united. The world is in difficulty but if we manage to get over our differences ... we can learn to make fewer mistakes," she told supporters, extending an olive branch to her rivals.
Argentina's economy is expected to grow eight per cent this year as high grains prices and strong demand in neighbouring Brazil boost revenues despite turmoil in the United States and Europe.
The winner on October 23 must get at least 45 per cent of the vote to avoid a runoff, or more than 40 per cent with a 10 percentage point lead over the second-place finisher in a race with multiple candidates.
In her victory speech, Fernandez referred to the looming global economic crisis and said politicians must ensure Argentina remains independent.
"We have to not only take care of our political democracy, but our economic democracy as well," she said.Kirchner's two main opponents, Alfonsin and Duhalde, a dissident from her own Parodist party, fared worse than expected, polling only around 12 percent each. The law prohibits them from forming an alliance.
"The serious campaign begins now. I'm sure we can win the elections in October," Alfonsin said.
Turnout was about 75 per cent of the nation's 29 million voters, who faced fines and bureaucratic hassles if they failed to cast ballots.
