A long-awaited expedition into an 18th-century shipwreck in the Caribbean Sea has reportedly begun.

The government of Colombia launched the deep-water expedition of the San José shipwreck, which is rumored to contain cargo worth billions of dollars, last week.

The galleon sank in 1708 en route to Cartagena, Colombia, after it was ambushed by an English squadron. Historians believe that roughly 600 people on the ship died, with very few survivors.

The shipwreck is believed to contain 11 million gold and silver coins, along with emeralds and other valuable cargo. The San José was carrying chests full of jewels and gold coins when it sank on its way to King Philip V of Spain.

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Split image of coins and ship part found in wreck

The expedition to the mythical San José shipwreck site began last week, officials say. (Reuters)

The shipwreck had a mythical reputation before it was discovered in 2015, at around 600 meters deep. It has been called the "Holy Grail of Shipwrecks" due to the vast amount of valuables it held.

Oceanographers have been able to map the shipwreck with robotic equipment attached to a naval ship. The robotic equipment has taken images of the wreck, showing several coins laying at the bottom of the shipwreck. Some of the coins were photographed scattered across the ocean floor with seashells. 

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Coins seen on bottom of shipwreck

Robot imaging shows that coins lay at the bottom of the shipwreck. (Reuters)

In February, the Colombian government announced that it was pouring $45 million into the exploration. The treasure is reportedly believed to be worth as much as $20 billion.

Colombia’s minister of culture previously said that the expedition's mission is to "claim the heritage elements for which the remains of the galleon should be valued."

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Vessels, vases found in shipwreck

The exact location of the San José shipwreck is a state secret. (Reuters)

"History is the treasure," minister Juan David Correa added.

The rights to the ship's sunken treasure have been claimed by Colombia, Spain and the United States. Its exact location in the Carribean is a state secret.

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Shells and coins on sea floor

Coins from the 1708 San José shipwreck were found scattered among sea shells on the ocean floor. (Reuters)

The Associated Press contributed to this report.

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