Federal cabinet reshuffle imminent

A federal cabinet reshuffle is imminent after two ministers stepped aside in one day.

Cities Minister Jamie Briggs resigned on Tuesday over an "error of professional judgment" involving a female public servant in a Hong Kong bar.

Mr Briggs has not detailed the incident other than to say it happened during an official visit in November.

Embattled frontbencher Mal Brough also stepped aside on Tuesday, succumbing to mounting pressure over his involvement in the James Ashby saga.

Mr Brough, the special minister of state and defence materials minister, is facing police investigations into whether he asked Mr Ashby, a former Peter Slipper staffer, to copy the former Speaker's diary.

The reshuffle is not expected to take place until early next year, amid speculation Deputy Prime Minister Warren Truss is preparing to announce his retirement.

Finance Minister Mathias Cormann and Defence Minister Marise Payne will fill Mr Brough's roles, while Environment Minister Greg Hunt will act as Cities Minister.