Robbers made off with an estimated $2.5 million from a mint in Mexico City after the vault was reportedly left open.
Police are searching for the perpetrators of the theft, which took place in broad daylight on one of the Mexican capital's most prestigious avenues, Avenida Reforma.
The heist is the latest development in a crime wave that has struck Mexico City in recent months as the security situation deteriorates across the country.
According to police reports, two thieves entered the mint, taking a security guard's gun and throwing him to the ground before making off with 1,567 gold coins from the vault, which was left open.
The "centenario" coins trade for 31,500 pesos ($1,610) each although their face value is just 50 pesos, according to Mexican bank Banorte.
This means the booty is worth around $2.5 million in total.
Police say they are studying security camera footage provided by the mint, which shows the suspects in action.
Initial investigations revealed that security protocols were not followed and the guard and two other staff members who were working at the time have been taken in for questioning, according to a statement from Mexico City's Secretariat of Public Security.