Up to 100,000 North Koreans have rallied in support for Kim Jong-un, after escalating tensions between US President Donald Trump and the North Korean leader.

A number of speeches were given at the hour-long event, organised by government officials at Pyongyang's Kim Il-sung Square on Saturday, including a repeat of Kim's statement the day before.

The North Korean leader said he will "consider with seriousness exercising a corresponding, highest-level hardline counter-measure in history", in response to Trump's address to the UN General Assembly on September 12.

Trump vowed to "totally destroy" North Korea if it threatens the US and its allies, labelling Kim a "rocket man" on a "suicide mission".

READ MORE: Trump insults make rocket attack 'inevitable': N Korea

Al Jazeera's Mike Hanna, reporting from the UN in New York, said: "It is a war of words with a very dangerous edge."

"We are talking about two, potentially nuclear, powers coming into a confrontation being egged on by a level rhetoric seldom seen and certainly not heard within the confines of the UN General Assembly," he added.

Tensions between the two have heightened in recent weeks, following the imposition of US-led UN Security Council sanctions on North Korea after its sixth, and most powerful, nuclear test to date on September 3.

US bombers flew close to North Korea's east coast on Saturday, going further north of the demilitarised zone separating North and South Korea than any US fighter jet or bomber has flown this century, according to Pentagon officials.

In Pyongyang, posters for Saturday's event included one showing missiles being dropped on Washington and the words "Korea's Answer".

Han Kwang-nam, an Environment Ministry official, told reporters: "We fear nothing, we are not afraid because we have the greatest ever general, the respected Supreme Leader Comrade Kim Jong-un. We will surely gain victory."

Government-organised rallies occur frequently in North Korea, and are intended to demonstrate popular support for Kim and his government.