Colombia has launched the exploration of the wreckage of a Spanish galleon that sank more than three centuries ago carrying an estimated $20 billion worth of treasure.

Juan David Correa, Colombia's culture minister, described the underwater expedition of the San José off the coast of Cartagena as "unprecedented," according to the BBC.

The vessel, which was destroyed during a 1708 battle with the British navy in the Caribbean Sea, has been called the "holy grail" of shipwrecks due to the trove of gold, silver and jewels it was bringing back to Spain. 

Correa announced the start of the project on Wednesday while declaring the site a "protected archaeological area," CBS News reported.

The first phase of the potentially lucrative effort reportedly involves using remote sensors to create images of the seabed around the remnants of the San José to determine what's down there.

The hoard was intended to help finance the War of Spanish Succession that followed the death of childless King Charles II, the last monarch of the Spanish Habsburg dynasty.

Both Colombia and Spain claim ownership of the San José, and the Colombian government is keeping the search location a secret on grounds of national security, the New York Times has reported.

A U.S.-based salvage company, Sea Search Armada, which claimed to have found the San José in 1981, is also seeking $10 million from Colombia in the United Nations' Permanent Court of Arbitration, according to CBS News.