PM seeks advice on minister's China trip

Prime Minister Malcolm Turnbull has asked the head of his department to advise him if one of his ministers breached the ministerial standards code over a private trip to China.

Labor is demanding an investigation of a trip Human Services Minister Stuart Robert took in August 2014 during which a close friend, who was also a Liberal Party donor, finalised a mining deal.

The opposition wants to know whether Mr Robert made the trip to attend a signing ceremony with mining company executive Paul Marks and Communist Party officials.

Mr Robert, who was then assistant minister for defence materiel, insists he attended in a private capacity and paid for the trip himself.

However, photographs and a statement on the website of Chinese government-owned company Minmetals suggest officials believed Mr Robert was representing Defence.

According to parliamentary records, Mr Robert is a shareholder in Mr Mark's companies.

Mr Turnbull on Monday told parliament the minister's personal leave was approved by then prime minister Tony Abbott in accordance with the usual procedures.

He confirmed the secretary of Prime Minister and Cabinet had been asked to provide him with advice.

"I deal with these matters very thoroughly and very seriously and in accordance with the code. That's what will be done," he said in answer to a question from Opposition Leader Bill Shorten.

Labor attempted to seek answers from Mr Robert during question time, but was ruled out of order by Speaker Tony Smith.

Questions about previous responsibilities could not be asked of a minister, he said.

Liberal Democrats senator David Leyonhjelm used the issue to call for reform to political donations.

A system that only allowed private donors would cut down on secretive donations, he said.

It would also stop voters being forced to fund campaigns for politicians "they wouldn't support in a million years".

"I find it really annoying that my taxes, for example, end up paying for (Greens leader) Richard Di Natale's re-election campaign," he told reporters in Canberra.

"I think that is much more offensive than a private donor contributing."