The victim had encountered two burglars in the interior court of a building housing the shop on Rue des Haudriettes, in the third arrondissement, when he arrived at 7am to start work, police said.
After an apparent struggle, the pair opened fire on the man, according to an online report from Le Parisien.
“We need to be very prudent as to the circumstances — we have only suppositions,” a source close to the investigation told the newspaper.
“But it seems the two burglars had waited for the employer to arrive in order to get in the shop and he resisted.”
Medics were unable to revive the man who died on the spot.
It appears the suspects, who fled the scene, did not take anything from the shop, located in a building that also houses a daycare centre.
Manuel Vallis, home affairs minister, and Sylvia Pinel, minister for arts and crafts, arrived at the scene of the crime, on a narrow-one way street, where residents were shocked by the news.
“I heard the cries,” a woman resident who lives in the building told Le Parisien.
“The employee was manhandled by two men,” said the resident.
She said that she heard the employee cry out to the men that he did not have keys to the shop.
“Everyone in the neighbourhood knew that he reconditioned gold here.”
The crime suppression squad of the Paris criminal investigation department is investigating the case.