"To my favourite Prime Minister. Great win," the US President scribbled on a photograph of them together.

Now Mr Trump has given Mr Najib the honour of being only the second south-east Asia leader he has hosted in the White House, despite that the US Department of Justice has filed lawsuits alleging the Malaysian leader received $US681 million of funds stolen from a state development fund called 1Malaysia Development Berhad (1MDB).

Mr Najib's handshake at the White House on Tuesday is sure to be spruiked by Malaysia's state-run media to show he can step foot on American soil without being arrested.

"It's a gigantic gift for Najib, who is suffering from a profound crisis of credibility at home as he prepares for a general election that is likely to come later this year," said Cynthia Gabriel, founder of the Centre to Combat Corruption and Cronyism in Kuala Lumpur.

Nurul Izzah Anwar, daughter of jailed opposition leader Anwar Ibrahim, said "the message the White House is sending is that it pays to be a kleptocrat and that the largest asset seizure in the history of the Department of Justice doesn't seem to matter in the great scheme of things".

Mr Anwar is among scores of Malaysian politicians, social activists, journalists and others who have been persecuted by Mr Najib's authoritarian regime.

On the eve of the White House meeting, Mr Najib pledged Malaysia will "stand shoulder to shoulder" with the US to fight terrorism and said his country shares Washington's concerns over North Korea.

During the talks Mr Trump is expected to raise China's growing influence in Southeast Asia and concerns over Beijing's build-up of islands in the flashpoint waters of the South China Sea.

But Mr Najib's critics say it is a mistake for Mr Trump to give the Malaysian leader a diplomatic plum at the White House that many world leaders would covet.

Investigations into the plundering of more than $US3.5 billion from 1MDB, which the Prime Minister set-up in 2009 and oversaw through his chairmanship of an advisory, are under way in at least six countries, including Singapore and Switzerland.

In August, the US Justice Department shifted its focus from civil proceedings to a criminal investigation into the missing money, much of which was allegedly laundered through the US by members of Mr Najib's family and his associates.

Mr Najib will be accompanied during his three-day US visit by his wife Rosmah Mansor, who is alleged to have received jewellery bought with 1MDB funds, including a $US27 million necklace with a 22-carat pink diamond pendant and 27 necklaces and bracelets.

The Department of Justice wants to seize them.

Ms Rosmah has not commented publicly on the allegations.

A close ally of successive Australian governments, Mr Najib denies any wrongdoing, claiming the hundreds of millions of dollars that turned up in his personal bank accounts were a gift from an unnamed Saudi prince, and that much of it was returned.

Mr Najib doesn't have to call an election until next year but some analysts believe he intends going to the polls within months, hoping to capitalise on disagreements in a newly formed opposition alliance that has yet to name its preferred prime minister.

Mr Najib and his supporters in the long-ruling United Malays National Organisation accuse opposition politicians - led by former prime minister Mahathir Mohamad - of hyping the 1MDB claims in an attempt to topple the government.

Dr Mahathir has criticised the Trump administration for inviting Mr Najib to the White House, saying "if President Trump wants to participate in our election, he can give his endorsement to the man who is described by the DOJ as a kleptocrat and a thief who has stolen money".

Vietnam's Prime Minister Nguyen Xuan Phuc is the only other south-east Asia leader to have met Mr Trump in the White House.

The President is scheduled to host Thai Prime Minister Prayuth Chan-ocha - who seized power in a 2014 coup - in the White House in October.

Philippine President Rodrigo Duterte, whose war on drugs has killed thousands of mostly poor Filipinos, has also been invited, although no date has been set for the visit.