North Korea displayed its submarine-launched ballistic missiles for the first time on Saturday ahead of a massive military parade in the capital, Pyongyang.
Weapons analysts said they believed some of the other missiles on display were new types of intercontinental ballistic missiles.
North Korea warned the United States on Saturday to end its "military hysteria" or face retaliation as a US aircraft carrier group steamed towards the region and the reclusive state marked the 105th anniversary of the birth of its founding father.
The North Korean ceremony began with a massive parade of military personnel and hardware through Pyongyang on Saturday morning to mark the birthday of Kim Il-sung, the revered founder of the nation.
Choe Ryong Hae, a close aide to Kim Jong-un, the current leader, addressed the packed square and reiterated the warning to the United States.
"If the United States wages reckless provocation against us, our revolutionary power will instantly counter with annihilating strike, and we will respond to all-out war with all-out war and to nuclear war with our style of nuclear strike warfare," he said.
State television showed live images of Kim Jong-un, the North Korean dictator, presiding over the march-past of thousands of military personnel through Kim Il-sung Square.
"The most powerful and cutting-edge strike and defence [capabilities] ... are lined up to put an end to the military supremacy claimed by imperialists," a television commentator said according to South Korea's Yonhap News.
Known as the Day of the Sun, the anniversary is the most important day on the North Korean regime's calendar, although this year's event comes at a time of heightened regional tensions.
There are clear indications that North Korea has completed preparations to carry out an underground nuclear test at its Punggye-ri proving grounds, while a US naval strike force, headed by the USS Carl Vinson, is approaching the Korean peninsula.
Both Pyongyang and Washington have intimated that they are willing and able to carry out a pre-emptive strike.
Quoting senior US intelligence officials, NBC News reported that Washington is prepared to launch a pre-emptive strike should a new North Korean nuclear test be imminent. US guided missile destroyers are on station in the Sear of Japan, the officials said, while heavy bombers are based on the Pacific island of Guam.
In an interview on Friday with the Associated Press in Pyongyang, Han Song-ryol, the North Korea vice foreign minister, said the US has become "more vicious and more aggressive" under President Donald Trump.
"We will go to war if they choose", he said, adding that the North is also ready to conduct a pre-emptive strike.
The North Korean government is apparently deeply concerned that a US attack is imminent, with Pravda reporting that Mr Kim has ordered one-quarter of Pyongyang's residents to evacuate the city immediately.
North Korea has also sent out new coded radio broadcasts, presumably to its agents in South Korea. Radio Pyongyang on Friday began broadcasting a series of page and line numbers from what South Korean intelligence believes is a book cipher that provides instructions to agents.
On Friday, the head of the Washington-based think tank The Institute for Science and International Security stated that North Korea has as many as 30 nuclear warheads at present but is stepping up production and is likely to have as many as 60 warheads by 2020.
Mr Trump was spending the weekend at his Mar-a-Lago club in Florida and was being kept informed of developments.
The Chinese and Russian foreign ministers, Wang Yi and Sergey Lavrov, discussed the situation by phone on Friday, with both countries then urging restraint.
Mr Wang said: "Lately, tensions have risen and 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."
Kremlin spokesman Dmitry Peskov said: "Moscow is watching with great concern the escalation of tensions on the Korean peninsula."
China enlists Russia help to avert crisis
China has sought to enlist Russia’s help to cool tensions over North Korea, amid fears among Beijing’s leaders that hostilities between the US and North Korea are imminent.
Foreign Minister Wang Yi made the appeal in a phone conversation with Sergey Lavrov, his Russian counterpart, after telling reporters that conflict could break out “at any moment”.
A statement on China's Foreign Ministry website said Mr Wang told the Russian diplomat: "China is ready to coordinate closely with Russia to help cool down as soon as possible the situation on the peninsula and encourage the parties concerned to resume dialogue.”
The comments were in relation to the six party talks, exchanges which centred on concerns over North Korea’s weapons program were launched in 2003 but stalled in 2009 when North Korea walked out. South Korea, Japan Russia, China and the United States were the other countries involved.
Beijing has this week pleaded with Pyongyang and Washington to find a peaceful solution to tensions which have escalated sharply amid fears that North Korea is set to carry out its sixth nuclear test since 2006.
US President Donald Trump sent an aircraft carrier strike group is to the region, heightening concerns in China that North Korea - an old ally - might provoke a strong response from Washington if it tested military hardware.
Mr Wang told reporters on Friday that a conflict could break out “at any moment” as he urged both sides to pull back from an “irreversible and unmanageable stage”.
Details of his phone call to Mr Lavrov came as Chinese state media warned Mr Trump that he would bring "more danger than security" to the world by unleashing US military firepower to solve crises.
The influential Global Times newspaper said Mr Trump “may go down in history as the ‘war president’” after his attacks in Syria and Afghanistan stunned the world.
The Global Times, which has close links to the ruling Communist Party, said Mr Trump has “demonstrated a certain level of obsession and pride toward US military prowess” with the missile strike against the recent Syrian regime and the dropping of the biggest ever non-nuclear bomb in US history on an Islamic State tunnel earlier this week.
“North Korea must have felt the shock wave traveling all the way from Afghanistan,” said the Global Times, which often reflects official opinion.
“It would be nice if the bomb could frighten Pyongyang but its actual impact may just be the opposite.” it added.
Pyongyang's “logic”, the newspaper said, is that its regime would be toppled in the same way that Saddam Hussein or Muammar Gaddafi fell if it fails to obtain weapons which could respond effectively to the firepower of its enemies.
“The "Mother of All Bombs" may once again misguide Pyongyang, leading it to believe that it is crucial to upgrade its explosives,” the editorial said.
“The US seems to enjoy a privilege to do whatever it likes. To the world, this could bring more danger than security.”
Mr Trump has been urging China to do more to confront North Korea over its build up of nuclear power, warning that the US will act unilaterally if Beijing was not willing to help.
"If China decides to help, that would be great," he tweeted on Tuesday. "If not, we will solve the problem without them!"
Analysts believe that Mr Trump is sending a message to China – not North Korea – with his confrontational language towards Pyongyang and his show of force with the aircraft carrier strike group – a force he called an “armada”.
The US president is not seeking to become embroiled in hostilities with Kim Jong-un’s regime, but to "harden" China's position towards the reclusive state by unnerving Beijing into reining in its wayward neighbour, they say.
John Delury, a senior fellow of the Center on U.S.-China Relations and an Assistant Professor of International Studies at Yonsei University, in Seoul, South Korea, warned that Mr Trump’s “bluff” could backfire.
“His coy allusions to a military 'solution' appear to be a bluff designed to harden Beijing's position against their ally in Pyongyang,” he said.
“Such hardening, however, usually proves cosmetic, if not illusory.
Prof Delury said Beijing would be seeking a diplomatic solution to the issue, rather than the “endless tightening of sanctions, or, as Trump seems wont to do, dangle the threat of war.”
Japan 'fully prepared'
Fumio Kishida, the Japanese foreign minister, told reporters in Tokyo that Japan needs to remain on alert and pointed out that Pyongyang may use other upcoming events to demonstrate its growing military might.
Mr Kishida said Japan need "to be fully prepared to take various measures", adding that the government is coordinating with the embassy in South Korea and other Japanese organisations across the country and has contingency plans in place.
The Ministry of Education has issued warnings for schools for Japanese nationals in South Korea and told management to monitor developments in light of the increased tensions on the peninsula. A similar warning has been issued for Japanese nationals visiting or living in South Korea.
"Honestly, I'm very worried about the situation because if it came to war, then no-one on the Korean peninsula would win", said Chung Hyon-suk, a Korean living in Japan but with relatives in both North and South Korea.
"I do not think things have been this bad since 1994", said Mrs Chung, referring to the crisis triggered when North Korea refused to permit inspectors from the International Atomic Energy Agency to inspect a plutonium reprocessing facility at Yongbyon.
"As we have seen time and time again, pressure and threats do not work at all with North Korea", she said. "It is part of the Korean national character to never give in to pressure and Mr Kim has his pride to protect."