Thierno Hamidou Diallo, 21, was shot in the chest by a police officer "as he was sitting on the balcony of his apartment"
A man was shot dead by police during a demonstration in Guinea that saw at least half a million people protest against alleged government corruption, officials said.
Several others were injured in the Conakry rally to denounce what they said was economic mismanagement by the government of President Alpha Conde, according to the same sources.
Opposition leader Cellou Dalein Diallo said 700,000 people had joined a 15-kilometre (nine mile) procession from the suburbs to the 28 Septembre stadium in the west African nation's capital.
Security forces said the number was closer to 500,000.
The fatality, named as Thierno Hamidou Diallo, 21, was shot in the chest by a police officer "as he was sitting on the balcony of his apartment" in the suburb of Bambeto, his brother Mamadou Dian Diallo said.
"I heard the shot myself but I never imagined it could have been aimed at my brother," said Diallo, who lost another of his brothers during a political protest in 2013.
An AFP reporter saw the body at the local Mere et Enfant (Mother and Child) hospital before it was transferred to a morgue.
Security minister Abdoul Kabele Camara said that violence had broken out in the late afternoon, leading to a police intervention in which "gunshots caused one serious injury and one fatality".
The police captain suspected of firing the shots had been identified and questioned, the minister said.
Aside from the fatality, twelve others were injured and six taken for questioning, the government said.
A doctor, speaking on condition of anonymity, said a number of injured had been treated at the Dixinn polyclinic, one of whom was in a coma.
- 'Death to dictatorship' -
Supporters of several opposition parties had gathered for the event, shouting "Alpha resign, Alpha that's enough, students unemployed, we want jobs", brandishing placards reading "death to dictatorship".
Union of Democratic Forces of Guinea leader Diallo hailed the huge turnout and said it proved the "rejection of dictatorship and poor governance of Mr Alpha Conde".
Diallo blamed Conde's government specifically for mishandling the massive Simandou iron ore project in the south of the country managed by British-Australian firm Rio Tinto, which he said meant Guineans could miss out on "decent jobs".
The government said in July the challenges of getting the project off the ground during a global iron ore glut were considerable but it would "do everything" to ensure it went on-stream.
Guinea's constitutional court in November 2015 formally confirmed Conde's re-election, dismissing opposition claims of vote-rigging and fraud.
It was only the second democratic presidential poll since Guinea gained independence from France in 1958.
In addition to focusing on the economy, rights campaigners have urged Conde to use his second term to intensify the fight against impunity, strengthen the judiciary and promote equal respect for the rights of all Guineans.
Despite the country being rich in minerals, most of the population in Guinea live in poverty and survive on less than one euro ($1.08) per day, according to the UN.