During WWII the Japanese Imperial Army systematically looted all the conquered Asian countries of their national treasures (This included; gold, silver, precious stones/gems, golden statues, etc.). During the earlier part of the war, WWII looted treasures were being shipped back to Japan for badly needed war finances. However, when American patrolling naval vessels made the shipping of these looted treasures to Japan much too risky to continue with due to almost certain loss, another plan was devised.

Investigative reports show that a great bulk of World War II treasures reached the Philippines from the latter part of 1943 through October, 1944, at that period when Field Marshall Count Terauchi was in-charge of the Japanese Imperial Forces in the Southeast area of the Pacific. He had ordered Admiral Masaharu (then over-all military commander of the Philippines before Yamashita) and several other Admirals and Generals (including Yamashita) that all war booties taken from their respective occupied territories comprising Java, Sumatra, Singapore, Malaysia, Thailand, Burma, and Northern India be collected and thereafter transferred to the Philippines.
Why So Much WWII Loot In The Philippines?
by Tony Wells
Japan had always considered the Philippine Islands to be a very important strategic location for military bases in Southeast Asia.

Unknown to the rest of the world, the Japanese Imperial Forces had a major plan for post war sovereign and the Philippine Archipelago was included in this elaborate scheme.

Once the shipping lanes became too dangerous due to American Naval vessels, almost all of the loot that the Japanese had accumulated thereafterwards was being channeled to the Philippines and buried.

Their ultimate plan was, that when the war was over they were going to withdraw forces from all the other Asian countries but try to maintain their colonial rule over the Philippine islands.
Under the banner of "Asia for Asians" they prescribed some reforms in the guise of nationalism. In hopes to win over the Philippine people, in 1943, the Japanese went as far as setting up a 'Philippine Republic', and installing a puppet government with the Judge Jose' Laurel as president.

By winning over the hearts of the Philippine people and later even granting them independence, the Japanese Forces hoped that they would be then regarded as 'hero's' by them. This would also allow them to put military bases there as a pretext of 'protection for the Philippine people'. In this way, they could remain in the Philippines for as long as they liked and take their time to re-excavate the stolen WWII loot at their leisure. It was a good plan but in the end it didn't work out - the Americans invaded the Philippines in October 1944.

However, before this U.S. invasion, the Japanese Imperial Forces were busy hiding and securing its stolen WW II loot. Elaborate tunnels were dug, some down to depths of a few hundred feet, to the final 'storage chambers'. Many of these tunnels were dug down to just below the water table during dry season, which would also be a deterrent to would-be future salvors.

Most, if not all of these tunnels, were booby-trapped and rigged with 1,000 and 2,000 pound WWII bombs and poisonous gas. This trick would also help keep the buried loot from falling into enemy hands. Detailed maps of the sites were drawn up on rectangular rice paper - all written in special treasure codes and the 2,000-year-old Japanese script known as 'Kungi'.
In most cases, POW labor was used to dig the intricate tunneling systems. In all cases, upon completion of securing the gold in the pits - the POW's were all executed and buried along with the treasures.

In some rare cases, Japanese officers even had their own soldiers killed and buried along with the treasure to protect their secret locations.

In all there were 172 'documented' Philippine burial sites (138 land and 34 water sites) left by the Japanese Imperial Forces. This is not to even mention the numerous 'private' burials of WWII loot by greedy officers and renegade soldiers.

There was still much treasure remaining to be buried when the U.S. abruptly invaded the islands. Japanese Forces took all of this with them up into the mountains in the northern Philippines and other
areas during their retreat, where it was all buried at many different locations.

It is estimated that the total worth of this war loot ranged up to 3 billion 1940's dollars - the equivalent of over $100 billion today. According to various post war estimates, the amount of gold bullion alone was 4,000 to 6,000 tons. Ex-president Ferdinand Marcos himself managed to recover several sites and that is how he became so wealthy.

The above information was collected from several books and other sources (including but not limited to) ;
Asian Loot (Charles C. McDougald)
The Gold of the Sun (Robert Curtis)
The Marcos Dynasty (Sterling Seagrave)
The Marcos Legacy Revisited: Raiders of the Lost Gold (Erick San Juan)
The World Atlas of Treasure (Derek Wilson)
The Yamamoto Dynasty (Sterling Seagrave)
Tracing Marcos' Gold - The True Story of the Yamashita's Treasure (D. Ahl Umali)
Plus... various newspaper articles and personal interviews.