North Korea has warned it will not be intimidated by Donald Trump's threats in an "unprecedented" letter sent to other countries.

"If Trump thinks that he would bring the DPRK, a nuclear power, to its knees through nuclear war threat, it will be a big miscalculation and an expression of ignorance," the letter said.

"Trump threatened to totally destroy the DPRK ... it is an extreme act of threatening to totally destroy the whole world."

The document was published by the Sydney Morning Herald and has been verified by Australia's foreign ministry.

Australia's prime minister dismissed it as a "rant", while the country's foreign minister said it showed diplomatic pressure from the international community was working.

It comes amid rising tensions between North Korea and the US, with Kim Jong Un's regime carrying out a number of ballistic missile and nuclear tests.

Mr Trump has threatened to "totally destroy" the country if needs be, describing Kim as "rocket man" on a suicide mission.

Titled "Open Letter to Parliaments of Different Countries", the letter was sent from Pyongyang's embassy in Indonesia to Australia's embassy in the country on 28 September.

It calls for "countries loving independence, peace and justice" to keep "sharp vigilance against the heinous and reckless moves" of Mr Trump, who is "trying to drive the world into a horrible nuclear disaster".

Australian Prime Minister Malcolm Turnbull said the letter was sent to "a lot of other countries".

He told Melbourne radio station 3AW: "It doesn't actually say anything about Australia so much. It's basically a rant about how bad Donald Trump is.

"I think that they are starting to feel the squeeze and that is because China, to its great credit, notwithstanding the long and very close history with North Korea, is part of the global sanctions including restricting oil exports into North Korea.

"So the tighter the economic sanctions are applied, the greater prospects we have of resolving that situation without a conflict."

Foreign minister Julie Bishop described the missive as an "unprecedented" communication.
She said: "It is not the way they usually publish their global messages.

"The collective strategy of imposing maximum diplomatic and economic pressure through sanctions on North Korea is working. This is a response to the pressure."