"The national-security environment that envelops our country has grown increasingly murky due to China's stepped-up activities in local waters and its rapid military expansion, along with North Korea's repeated militaristic provocations," Mr. Noda said in a speech at a Japanese Air Self-Defense Force base north of Tokyo.
The Japanese leader cited the threats posed by China and North Korea in a call for Japan's Self-Defense Forces to stand ready for future national emergencies.
While Mr. Noda, who became prime minister in early September, has emphasized the lack of transparency in China's burgeoning military budget before, these are his first remarks that bear directly on Japan's Self-Defense Forces and on the role he expects them to play during his tenure as premier.
The remarks come less than a year after Japan released a new set of strategic defense guidelines for the next decade calling for a more "dynamic" and less passive approach to security. The National Defense Program Guidelines, formally announced last December, signal a major shift away from a Cold War-era focus on Russia in the north to a new orientation aimed at China and at protecting sea lanes south of Japan.
Japan's disputes with China over territory and wartime history have continued to strain relations between the two countries despite the deepening trade ties between Asia's two largest economies.
In March, China said it was boosting its military spending 13% over the next 12 months, adding to what is already the world's second-largest defense budget after the U.S.'s. By contrast, Japan's spending on defense has fallen each year for almost a decade.
Taking advantage of its growing military might, Beijing has shown a growing tendency to flex its muscles to further its territorial claims.
Japan and North Korea also have plenty of wartime history, while the long-running issue of Japanese nationals abducted by Pyongyang continues to smolder without resolution.
Perhaps of more concern on a military level are North Korea's refusal to rejoin six-party talks on its nuclear-weapons program, its repeated missile testing, including a long-range Taepodong-2 in April 2009, and last November's shelling of the South Korean island of Yeonpyeong, in which four people, including two civilians, were killed.
Tensions between Japan and China flared in September last year when a Chinese fishing boat crashed into Japan coast guard patrol boats in the potentially resource-rich waters near the Senkaku Islands. The islands are at the center of a territorial dispute between the two nations and also Taiwan.
When Japan detained the Chinese captain of the boat for more than two weeks after the collision, it sparked nationalist protests in China and Japan, straining diplomatic ties.
The tensions are also playing out in the skies of East Asia. On Thursday, Japan's defense ministry said the scrambling of Air Self-Defense Force jets to deal with Chinese aircraft flying through Japanese airspace had increased significantly in recent months.
Mr. Noda, the son of a career soldier in the Self-Defense Forces, has rubbed Beijing the wrong way by reiterating in August—during his campaign to become prime minister—his view that Japan's wartime leaders, convicted at the international tribunal at the end of World War II, weren't technically criminals.
The prime minister made his latest comments at an annual review of troops and military equipment, which is hosted on a rotating basis by each of Japan's three SDF branches.
He praised the SDF for their rescue and relief efforts after the March earthquake and tsunami that devastated hundreds of miles of coastline in northeast Japan. He also thanked the U.S. military for its supporting role in those aid activities, a mission dubbed Operation Tomodachi, which means friend in Japanese. "The importance of the U.S.-Japan security alliance remains unchanged" as a pillar of stability in the Asia-Pacific region, he said.
The prime minister singled out for special praise the Japanese military's efforts to deal with the crisis at the Fukushima Daiichi nuclear plant in the days immediately following the March disaster. He noted the forces' attempt to douse the reactors with sea water by helicopter and decontamination and civilian evacuation activities around the damaged plant.
This year, Japan's Air Self-Defense Force conducted the memorial event, the sixth time it has done so since the first review took place in 1953.
Among the aircraft on display were F-2 and F-4 fighter jets. Japan's contingent of F-15 fighters was grounded, however, because of an investigation into an F-15's dropping of a fuel tank during a training exercise earlier this month.
Last month, Japan moved a step closer to buying a new generation of jet fighters to replace the F-4, after it accepted bids by three of the world's biggest defense contractors for what is expected to be a deal valued at several billion dollars
