TOKYO (Kyodo) -- The Japanese Self-Defense Forces and the U.S. military began a joint exercise Wednesday across Japan to ratchet up interoperability amid China's intensifying military assertiveness in the Indo-Pacific region.

The biennial field training exercise, dubbed Keen Sword, is expected to involve some 33,000 Japanese and 12,000 U.S. personnel, according to Japan's Defense Ministry. It will also involve about 30 Japanese vessels and 250 aircraft and about 10 U.S. vessels and 120 aircraft.

"We have a strong sense of urgency given that we cannot rule out the possibility of a grave situation similar to Ukraine occurring in the vicinity of our country. We need to do whatever it takes to prevent and deter such a situation from happening," Gen. Yoshihide Yoshida, the top uniformed officer of the SDF, told a press conference Tuesday.

The joint press conference with Adm. Steve Koehler, commander of U.S. Pacific Fleet, was held at a U.S. military base in Nagasaki Prefecture.

Originating in 1986, Keen Sword is scheduled to run through Nov. 1 this year and will be the SDF's largest field training exercise in the current fiscal year through March. Australian and Canadian forces will also join some parts of it.

The exercise covers fields including operating an integrated air and missile defense system, island defense and cross-domain operations involving space, cybersecurity and electromagnetic waves, according to the ministry and the U.S. military.

The two sides will also establish a joint medical hub in Okinawa during the exercise to practice facility management, treatment and patient transfer.

They will train to airlift casualties to major SDF hospitals, among other facilities, on the main island of Honshu from remote southwestern islands by aircraft.

Security conditions surrounding Japan have become increasingly severe, with the country alarmed by recent airspace breaches by China and Russia, as well as other military activities around the country, prompting an Air SDF fighter jet to fire a signal flare in September for the first time.