Defence Minister Itsunori Onodera, who has previously stressed "Dawn Blitz" was not aimed at China, told reporters that the joint exercise was designed to "significantly contribute to our capability".
It is the first time all the three arms of Japan's Self Defence Forces -- army, navy and airforce have taken part together in a drill based on the US mainland.
Of some 1,000 Japanese personnel participating in the multi-national amphibious exercise, the bulk are naval troops from three destroyers of the Maritime Self Defence Force, according to Japanese media.
The exercise comes as Beijing and Tokyo remain at loggerheads over the ownership of Tokyo-administered islands in the East China Sea, with frequent confrontations between official ships from the two sides.
The United States has repeatedly said it did not take a position on the sovereignty of the Senkaku islands, which China calls the Diaoyus, but has said they are covered by a mutual defence treaty.