Donald Trump has announced he has replaced National Security Advisor HR McMaster with former Bush official turned Fox News commentator John Bolton.

The major staffing shake-up was made public in a tweet by the president just before 9.30am AEDT.

"I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor," Trump tweeted.

"I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9."

McMaster , a former general, has not commented on his surprise ousting.

Bolton is an unusual choice for Trump, though the appointment has been rumoured for weeks.

While Trump ran as a vociferous critic of the war in Iraq, Bolton was one of the Bush Administration's most vocal advocates of the war.

HR McMaster and Donald Trump. (AAP) (AAP)

Last month Bolton wrote an article in the Wall Street Journal calling for a preemptive strike on North Korea.

He served as United States ambassador to the United Nations from 2005 to 2006.

He is currently a commentator on Fox News.

Obama White House staffer Tommy Vietor, now a popular podcast host, criticised the decision.

John Bolton. (AAP) (AAP)

"John Bolton as National Security Advisor is the worst case scenario," he tweeted.

"Trump campaigned against the disastrous decision to invade Iraq, but Bolton remains unrepentant and is now arguing to strike North Korea. Disaster."

McMaster was a popular choice as National Security Advisor, with the Senate overwhelmingly approving of his appointment.

But the relationship between McMaster and Trump quickly became strained.

Last month Trump sharply rebuked McMaster after the general said Russian interference in the US election was beyond dispute.

McMaster's dismissal comes a week after Secretary of State Rex Tillerson was fired via Twitter.

The National Security Advisor is a top White House role, with the appointee tasked with counselling the president on global and military matters.

Previous advisors include Henry Kissinger, Colin Powell and Condoleeza Rice.

Bolton is Trump's third National Security Advisor in 14 months. His first appointment, Michael Flynn , was sacked after 24 days in the position.