Andrew Broad is repaying tax-payer funded flights to see 'sugar baby'

Under-siege Nationals MP Andrew Broad is repaying more than $400 of taxpayer-funds spent on a connecting flight to see his "sugar baby".

Mr Broad flew from Melbourne to Hong Kong to meet with the woman known as "Sweet Sophia Rose".

But he used taxpayer-funded travel allowance to fly from his base in Mildura, to Melbourne.

9NEWS has been told he is in the process of paying the money.

Coalition colleague Treasurer Josh Frydenberg called the alleged conduct of Mr Broad "unacceptable".

Mr Broad resigned as an Assistant Minister after claims published in the New Idea magazine revealed he sent salacious messages to a younger woman he met through a so-called "sugar-daddy" website.

The move comes with the Herald Sun reporting at least three women have contacted the National Party in the past year about Mr Broad’s behaviour.

Appearing on the Today Show this morning, the Treasurer said "what is very clear is that this conduct was unacceptable, he has resigned. That was the right thing to do."

Last night, it was revealed his party's leader, Deputy Prime Minister Michael McCormack, knew about the scandal for almost six weeks.

He told journalists earlier in the day he had known for "a couple of weeks", and advised Mr Broad to contact the Australian Federal Police in relation to concerns he had about the woman's conduct.

But after the AFP confirmed it had received a report on November 8, and found no Australian criminal offence had been detected, Mr McCormack was forced to clarify.

"When asked about the timing of Mr Broad's notification to me of allegations against him in the media, I responded "a couple of weeks ago" as I thought that was approximately the timing of that call", Mr McCormack said in a statement.

Mr Frydenberg was asked if Mr McCormack should've acted sooner.

"I think Michael McCormack was trying to work through this issue," Mr Frydenberg said.

But he added, "As soon as the Prime Minister heard he acted straight away."

9NEWS understands the Prime Minister's office first became aware of the scandal yesterday morning.

Fresh questions have been raised about Mr Broad's use of taxpayer-funded travel.