Pyongyang has held a massive military parade
North Korea has warned the US to end its "military hysteria" or face retaliation - as an American strike group, including an aircraft carrier, steams towards the region.
Pyongyang issued the warning as it displayed new submarine-based ballistic missiles in a massive military parade in the city.
The reclusive state said it was prepared to respond to any attacks with "nuclear attacks of our own style", as tension mounted in the region.
China, Pyongyang's sole major ally, has warned that the tensions must be stopped from reaching an "irreversible and unmanageable stage".
Chinese Foreign Minister Wang Yi said: "We call on all parties to refrain from provoking and threatening each other.
"One has the feeling that a conflict could break out at any moment.
"Once a war really happens, the result will be nothing but multiple loss. No one can become a winner."
On Saturday, North Korean leader Kim Jong-Un arrived at Pyongyang's main Kim Il Sung Square, named after his grandfather.
He led a military parade marking the "Day of the Sun", the 105th birthday of the state's founding father Kim Il-Sung.
Goose-stepping soldiers and marching bands filled the square, next to the Taedonggang River that flows through Pyongyang.
Tanks, multiple rocket launch systems and other weapons followed, while single-engine planes flew in a 105 formation overhead.
South Korea's military said it believed some of the missiles in the parade included new types of intercontinental ballistic missiles (ICBM).
The North has said it has developed and would launch a missile that can strike the US mainland.
"All the brigandish provocative moves of the US in the political, economic and military fields pursuant to its hostile policy toward the DPRK will thoroughly be foiled through the toughest counteraction of the army and people of the DPRK," a spokesman for the General Staff of the Korean People's Army said.
DPRK stands for the official name of North Korea, the Democratic People's Republic of Korea.
"Our toughest counteraction against the US and its vassal forces will be taken in such a merciless manner as not to allow the aggressors to survive," the military spokesman continued.
The US has warned that the policy of "strategic patience" with North Korea is over.
Pyongyang has conducted several missile and nuclear tests in defiance of UN and unilateral sanctions.
US Vice President Mike Pence travels to South Korea on Sunday for a long-planned 10-day tour of Asia.
In the past two weeks, Donald Trump has shown his willingness to resort to military methods.
He ordered a missile attack on Syria in retaliation for a suspected chemical weapons attack.
And earlier this week he dropped the "mother of all bombs" on caves used by Islamic State in Afghanistan.