Microsoft cofounder Paul Allen says he has found the Imperial Japanese Navy's biggest warship at the bottom of the sea in the Philippines, 70 years after US forces sank it.

Allen posted a photo on Twitter on Tuesday of the World War II battleship Musashi's rusty bow, which bore the Japanese empire's Chrysanthemum seal.

WW2 Battleship Musashi sank 1944 is FOUND > 1K M deep by MY Octopus Sibuyan sea, bow Chrysanthemum, huge anchor. pic.twitter.com/b9ZMA0icI8 — Paul Allen (@PaulGAllen) March 2, 2015

RIP crew of Musashi, appx 1023 lost. The pic of the valve 1st confirmation of Japanese origin (clues 2 use apprec). pic.twitter.com/BcJgkhWskb — Paul Allen (@PaulGAllen) March 2, 2015

Musashi expedition captures amazing video of remarkable WWII warship http://t.co/Ry1NZ4nveW pic.twitter.com/X27GTJMiKl — Paul Allen (@PaulGAllen) March 4, 2015

The American billionaire, who has also pursued space exploration, said his luxury yacht and exploration ship, the M/Y Octopus, found the Musashi one kilometer deep on the floor of the Sibuyan Sea.

The Octopus' remote operated probe Octo ROV located the Musashi on Monday, according to Allen's website. The Octopus is also outfitted with an exploration submarine.

"RIP (rest in peace) crew of Musashi, approximately 1,023 (lives) lost," Allen said in another tweet.

Allen also posted a photo of a valve from the wreckage, which he described as the "first confirmation" that it was of Japanese origin.

He said on Twitter he would soon post video of the ship's catapult and valve areas.

The Sibuyan Sea, at the heart of the Philippines' central Visayas islands, covers busy shipping lanes and lies on the path of most tropical storms that cross the country from the Pacific Ocean.

American warplanes sank the Musashi in the Sibuyan Sea on October 24, 1944, at the height of the Battle of Leyte Gulf, considered the largest naval encounter of World War II in which US and Australian forces defeated the Japanese.

The Musashi was a "mighty battleship" with "mammoth 18-inch guns," according to the US Navy's website.

Its twin ship, the Yamato, was damaged in the fighting, according to the US Navy, and American warships finally sank it a year later as it attempted to reach Okinawa.

The Seattle-born Allen, 62, who founded Microsoft with Bill Gates in 1975, is the 51st-richest person in the world, with a net worth of $17.5 billion, according to Forbes Magazine.

In 2012, Allen loaned the same ship that located the Musashi to the British government to locate HMS Hood bell from the bottom of the Denmark Strait. The search was eventually called off because of bad weather.

Allen is also working on a project called Stratolaunch, which aims to put "cost-effective" cargo and manned missions into space.

He launched SpaceShipOne, the first privately built spacecraft, into suborbital space in 2004.

Allen did not immediately reply to AFP's request for comment via Twitter.

Representatives for the Philippines' navy and coast guard told AFP they were not informed of the discovery.