US Secretary of State John Kerry told Japan Sunday the United States would protect it from North Korea's threats, after securing a commitment from China to rein in the unpredictable regime.

After a meeting with Japanese Foreign Minister Fumio Kishida in Tokyo, where Patriot missiles have been deployed in anticipation of a missile launch by the North, Kerry pledged the US would backstop its ally.

"The United States is fully committed to the defence of Japan," Kerry told a joint press conference with Fumio Kishida, Japan's Foreign Minister, in Tokyo.

Kerry's comments came after the Korean Central News Agency said Friday any attempt by Japan to shoot down a missile would result in war that would see Tokyo "consumed in nuclear flames".

"Japan is always in the cross-hairs of our revolutionary army and if Japan makes a slightest move, the spark of war will touch Japan first," KCNA said in a commentary.

The Asian leg of Kerry's 10-day tour has seen him move through Seoul and Beijing, with Washington keen to press home the need for a united front against Pyongyang's erratic and bellicose behaviour.

He found a sympathetic ear in Japan, where Prime Minister Shinzo Abe, who will hold talks with Kerry on Monday, said Pyongyang had to realise it was harming itself by being "provocative".

There are fears the launch could come on Monday, the anniversary of the birth of the North's late founder Kim Il-Sung. The presence of Kerry in the region, ensuring maximum publicity, may also appeal to the regime.

"The government will do its utmost to protect the lives and safety of the Japanese people," Abe told local reporters during a visit to Iwo To, better known as Iwo Jima, where he attended a war memorial service.

"The international community has to be united and make North Korea realise that their provocative acts do not bring any benefit to North Korea," Abe said, according to national broadcaster NHK.

"Japan wants to coordinate with the United States, South Korea, China and Russia and convey the message to North Korea that it must not repeat its provocations and must not launch missiles."

Kerry's arrival in Japan, where he will stay until Monday afternoon, follows an intense day of diplomacy Saturday in Beijing, where he warned Chinese leaders including President Xi Jinping that the stakes for global and regional security were high.

China is Pyongyang's sole major ally and backer, and is widely seen as the only country with leverage to influence its actions -- although it is reluctant to risk destabilising the regime.

The top US diplomat hailed Saturday's joint commitment from Chinese and US leaders to work together to dial down the tensions as "unprecedented".

"The importance of the visit yesterday really cannot be overstated," Kerry told US embassy staff in Beijing before flying to Tokyo.

"This is a critical time needless to say, being able to speak directly to my Chinese counterpart and try to focus on some very critical issues is of major importance."

China's State Councillor Yang Jiechi, who is in charge of Beijing's foreign policy, said his nation "will work with other relevant parties including the United States to play a constructive role".

The US Chairman of the Joint Chiefs of Staff Martin Dempsey this month will lead a delegation to Beijing to follow up on the talks and ensure they were not just rhetoric, Kerry said.

China is estimated to provide as much as 90 percent of its neighbour's energy imports, 80 percent of its consumer goods and 45 percent of its food, according to the US-based Council on Foreign Relations.

But analysts say it is wary of pushing too hard for fear of a regime collapse sending waves of hungry refugees flooding into China and ultimately leading to a reunified Korea allied with the United States right on its border.

During his whirlwind tour, Kerry paid his first ever visit to South Korea meeting new President Park Geun-Hye on Friday, where he offered public support for her plans to initiate some trust-building with the North.

But Pyongyang on Sunday dismissed the South's offer for talks on the future of the Kaesong joint industrial zone, after the North announced it would withdraw its 53,000 workers and suspend operations.