The attack, which the economy minister called an assassination attempt, comes at a time of acute political and social frictions inside Argentina.

It happened as Fernandez de Kirchner stepped out of a car outside her Buenos Aires home, where hundreds of supporters had gathered. Video footage showed a man holding a pistol next to her head.

President Alberto Fernandez said the gun had been loaded with five bullets.

"This is the most serious event we have gone through since Argentina returned to democracy," he said in a televised address, referring to the 1983 end of military rule.

"A man pointed a firearm at her head and pulled the trigger. Cristina is still alive because, for some reason yet to be confirmed, the gun ... did not fire."

Her suspected assailant, whom authorities identified as a 35-year-old man of Brazilian origin, was quickly arrested by police and the weapon seized.

A divisive figure inside Argentina who was president between 2007 and 2015, Fernandez de Kirchner is on trial for corruption linked to public contracts awarded in the early 2000s.

She could face a 12-year sentence and possible disqualification from public office if convicted on the charges, which she denies. She has been widely expected to run for the Senate and possibly the presidency again next year.

Argentina is also mired in a deep economic crisis driven by spiralling debt levels and inflation that has triggered street protests.

"When hate and violence prevail over debate, societies are destroyed and situations like these arise," tweeted Economy Minister Sergio Massa, who was recently appointed to tackle the national crisis.

Heads of state and political allies around the region, including Chilean President Gabriel Boric, Venezuela's Nicolas Maduro, Peru's Pedro Castillo and Brazilian presidential candidate Luiz Inacio Lula da Silva, also denounced the attack.

They expressed solidarity with Fernandez de Kirchner and voiced relief that she had not been hurt.