Chinese President Xi Jinping urged "restraint" over North Korea in a phone call with Donald Trump Monday, as Japan joined exercises with an American supercarrier heading to the Korean peninsula.

The US leader has repeatedly called on China, the North's sole major ally, to do more to rein in Pyongyang, as tensions in the region soar amid speculation it will conduct another nuclear test.

"[China] hopes that the relevant parties can maintain restraint and avoid actions that would increase tensions in the Korean peninsula," Xi said, according to the foreign ministry.

"The only way to realize denuclearization in the Korean peninsula and quickly resolve North Korea's nuclear problem is for each relevant party to fulfil its duties."

"The international situation is rapidly changing, it is essential that China and the US maintain a close contact and exchange opinions on important matters in a timely manner," Xi told Trump.

Trump also spoke to Japanese Prime Minister Shinzō Abe on Monday, discussing the joint drills under way between the US carrier Carl Vinson and Japan's Maritime Self-Defense Force.

Sales of nuclear shelters and radiation-blocking air purifiers have surged in Japan in recent weeks as North Korea has pressed ahead with missile tests in defiance of international sanctions.

"We completely agreed that we strongly demand restraint by North Korea, which has repeatedly made dangerous provocative actions," Abe told reporters after the call.

Tensions have soared in recent months as North Korean missile tests have brought ever-more bellicose warnings from Trump's administration and repeated demands for China do more to help.

Despite its longstanding ties with the North, China has stepped up pressure, announcing in February that it was halting all imports of coal from North Korea, a crucial earner for Pyongyang, for the rest of the year.

It also issued a stern warning earlier this month that a conflict over North Korea could break out "at any moment".

The comments came ahead of a failed missile test a day after the 105th anniversary of the birth of North Korea's founder Kim Il-Sung.

US Vice President Mike Pence said Saturday that the USS Vinson and its strike group would arrive in the Sea of Japan "in a matter of days".

South Korea also said it was considering drills with the carrier group, which is currently conducting joint exercises with Japan in the Philippine Sea.

The North's ruling party newspaper on Monday called the Vinson's deployment "undisguised military blackmail".

"Such threat may startle a jellyfish, but can never work on the DPRK" it wrote.

The new US President has indicated he will not allow North Korea to achieve its goal of developing an intercontinental ballistic missile capable of delivering a nuclear warhead to the western United States.

Now North Korea marks the founding anniversary of its military today, and South Korea and its allies are bracing for the possibility that it could conduct another nuclear test or launch an intercontinental ballistic missile for the first time.

North Korea often marks significant dates by displaying its military capability. It so far has carried out five nuclear tests.

Recent U.S. commercial satellite images indicate increased activity around North Korea's nuclear test site, and third-generation dictator Kim Jong Un has said the country's preparation for an ICBM launch is in its "final stage."

South Korea's Defense Ministry has said North Korea appears ready to conduct such "strategic provocations" at any time. South Korean Prime Minister Hwang Kyo-ahn, the country's acting leader in place of ousted President Park Geun-hye, who has been arrested over corruption allegations, has instructed his military to strengthen its "immediate response posture" in case North Korea does something significant on Tuesday's anniversary.