Shadow attorney-general Mark Dreyfus has referred Stuart Robert's China trip to the Australian Federal Police, asking them to launch an investigation into whether the former minister intended to benefit from the visit.

Key points: Dreyfus writes to AFP commissioner Andrew Colvin asking for investigation into Robert's China trip

Dreyfus writes to AFP commissioner Andrew Colvin asking for investigation into Robert's China trip Says conduct may have involved "serious criminality"

Says conduct may have involved "serious criminality" Cites criminal code section dealing with "abuse of public office"

Mr Robert announced he would step down from the frontbench on Friday, after an internal investigation revealed he had shares in a trust linked to mining company Nimrod Resources, whose chairman Paul Marks is a generous Liberal donor.

Labor had called for Mr Robert to be sacked over the trip in 2014, during which he appeared in a signing ceremony for a mining deal between Nimrod Resources and a Chinese business.

In a letter to AFP commissioner Andrew Colvin, Mr Dreyfus argued the "publicly reported facts" about Mr Robert's trip showed his conduct "may also have involved serious criminality".

"It is clear that Mr Robert sought to benefit Mr Marks, a significant Liberal donor, but the revelation that Mr Robert himself stood to gain financially through his shareholdings in a company related to Nimrod is even more serious," Mr Dreyfus wrote.

"The Prime Minister has been careful to say only that this created an 'impression' that Mr Robert stood to gain personally from his trip.

"Whether he intended to do so now merits a proper police investigation."

Mr Dreyfus cited section 142.2 of the criminal code, which deals with the "abuse of public office".

He told the ABC that Mr Robert's shares in Nimrod Resources took the matter "to a whole new level".

"This is a matter of fact: if he had shares in Nimrod Resources, the mining company whose signing ceremony he was attending in Beijing, then he has a direct interest," he said.

"He stands to personally profit from the activities of that mining company and that takes it into the area of a potential criminal offence, namely abuse of his public office."

Mr Robert resigned from his position as Minister for Veterans' Affairs and Human Services last week, asking Prime Minister Malcolm Turnbull not to consider him in his ministerial reshuffle, confirmed at the weekend.

He had previously said he travelled to China in a personal capacity and that he was confident he did not act inappropriately.

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Liberal Minister Josh Frydenberg would not be drawn on the issue when asked today, telling the ABC that "Stuart Robert is a colleague of mine, he is in the Parliament and he has paid a very high price".

Mr Robert was one of several ministers dumped from the frontbench in recent months.

Jamie Briggs resigned as Minister for Cities and Built Environment late last year following a late-night incident involving a female public servant in a Hong Kong bar.

Mal Brough also gave up the role of Special Minister of State on Saturday after standing aside last year while the AFP continued its investigation into the James Ashby and Peter Slipper affair.

Mr Turnbull's new ministry will be sworn in on Thursday.

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