Senior immigration officials told the hearing on Friday that 14 people had been identified as having applied for visas through Mr Maguire's associates, including nine who were still in Australia.

Officials were unable to say how many of the nine currently had permanent residency status.

Department of Immigration and Border Protection Secretary Michael Pezzullo told the hearing that people who acted "fraudulently" could be stripped of visas or citizenship.

Mr Pezzullo said visas associated with Mr Maguire's scheme were subject to "a criminal investigation" in relation to the Australian Border Force.

"If visas have been granted in relation to false credentials or matters fraudulently otherwise, those visas will be cancelled as general principle," he said.

"Even in the cases where citizenship has been gained, the act has long allowed for the stripping of citizenship and we will come down in a very tough-minded way once we have done our process."

Mr Pezzullo told Senate Estimates in October that Home Affairs was assisting ICAC's investigation.

Labor NSW Senator Kristina Keneally asked senior Home Affairs officials at the estimates hearing on Friday how many people were being investigated following the Independent Commission Against Corruption's hearings into Mr Maguire.

Home Affairs Deputy Secretary for Immigration and Settlement Services Andrew Kefford told the hearing that nine of the 14 people identified by ICAC were still "onshore" in Australia.

"The advice I have is that there are three citizens," Mr Kefford said.

"We have got 14 cases of visa fraud, nine of them are still onshore and three of them have become citizens? Is that your evidence?" Senator Keneally asked.

Mr Kefford agreed this was the case.

"The 14 individuals named [by ICAC] we're still examining ... we still have to go through the administrative process of determining and there is under the act the ability to cancel visas where fraud is proven."

Senator Keneally said that was "extraordinary".

"How did this get to the point where three people become citizens of the country when it appears, according to Mr Maguire, that he fraudulently got them into Australia?" she asked.

"This was a Liberal Member of Parliament that was fraudulently selling visas and this has progressed to three people becoming citizens. What kind of border control is this?"

In October, Mr Maguire admitted to suggestions at ICAC that he committed a "breach of public trust" by involving his own constituents in a cash-for-visas "scam".

Mr Maguire agreed he was told by a Riverina business and by his own associates that Chinese visa applicants were not turning up to contracted work but he continued to collect thousands of dollars in cash from the scheme.

"You realised from an early point in time that there was a very serious risk that this was a scam, is that right?" Counsel assisting ICAC Scott Robertson asked.

"Yes," Mr Maguire replied.

Senator Keneally asked how the Wagga RSL was able to determine that a proposal, linked to Mr Maguire, to hire Chinese visa applicants was "a bit dodgy" after just one meeting but Border Force had allowed the scam to continue for seven years.

Home Affairs Deputy Secretary for Immigration and Settlement Services Andrew Kefford replied that the agency "relies on the information that we have to hand".

"What might be able to be seen with hindsight is not necessarily obvious at the time," he said.

Mr Kefford said border agencies were "following the web" of visa issues raised by ICAC public hearings into Mr Maguire.

Australian Border Force Commissioner Michael Outram told Senate Estimates that his agency started investigating visa issues related to Mr Maguire on October 13 following a referral on October 8 from ICAC.

"We're looking at offending under the Migration Act," Mr Outram said.