Malaysia on Tuesday deported two Australian journalists who were detained after trying to question Prime Minister Najib Razak about multiple scandals swirling around him.

Najib's government has waged a months-long campaign to stifle scrutiny of the allegations of massive corruption that he faces, sparking warnings that press freedom was under assault.

He is battling accusations that billions of dollars were stolen from a state-owned fund he established in 2009, and is under pressure to fully explain his acceptance of a mysterious $681 million overseas payment.

Australian journalists Linton Besser and Louie Eroglu had been detained overnight in the city of Kuching on Saturday, then released but barred from leaving Malaysia pending possible charges.

But authorities abruptly dropped plans to charge them Tuesday and they flew to Singapore shortly after, their local attorney Albert Tang said.

‘Obviously, they are relieved,’ Tang told AFP.

Malaysian police have accused the two men, from the Australian Broadcasting Corporation (ABC), of crossing a security line, saying they ‘aggressively tried to approach the prime minister.’

They had faced possible charges of ‘obstructing a public servant’.

Najib, 62, also faces lingering questions over the murder in 2006 of a Mongolian woman by two of his bodyguards.

The victim, Altantuya Shaariibuu, was reputedly at the centre of alleged multi-million-dollar kickbacks in the 2002 purchase of French submarines when Najib was defence minister.

Government critics and anti-corruption activists have long alleged that the bodyguards -- who have been sentenced to death over the murder -- were ordered by higher-ups to kill Altantuya, possibly to silence her.

Najib denies any involvement.

- 'Roller coaster' experience -

Besser had tried to question Najib on Saturday night as the prime minister visited a mosque in Kuching, capital of Malaysia's Sarawak state on Borneo island.

Speaking at Kuching's airport Tuesday, Besser told reporters it had been a ‘roller coaster few days’ but declined further comment as the pair hurried to board their flight out.

Australian Foreign Minister Julie Bishop on Monday had expressed concern, saying journalists should be allowed to work unhindered.

ABC denies Malaysia's accusations against the journalists.

‘They did nothing wrong in Kuching. They were doing journalism,’ ABC News director Gaven Morris said, adding that he was ‘very glad and relieved’ at the outcome.

‘This incident has demonstrated again why it is vital to defend media freedom, including the right to question authority.’

Najib and the state firm, 1Malaysia Development Berhad (1MDB), deny suggestions that the $681 million payment he received was siphoned from the now debt-stricken company.

His government says it was a ‘personal donation’ from the Saudi royal family, most of which was returned. The claimed Saudi link is widely ridiculed in Malaysia as false.

The government has moved to curb investigations and purge ruling-party critics who have called for transparency, and has repeatedly pressured media outlets that report on the affair.

In the most recent incident, authorities blocked access to a leading news portal after it ran a report implying guilt on Najib's part.

The site, the Malaysian Insider, was shut down for good on Monday by its parent company.