The head of Customs has warned there will be further arrests linked to a long-running corruption investigation into the agency.

Eight people, including two Customs employees and a quarantine officer, have so far been arrested and charged over allegations relating to the importation of drugs.

Acting Customs chief executive Michael Pezzullo has told a Senate hearing the anti-corruption crackdown is ongoing and further action will be taken.

"Further arrests will be made - including of other Customs and Border Protection officers," Mr Pezzullo told senators.

"Separate from criminal proceedings, disciplinary proceedings are being initiated against a number of officers.

"This [Senate] committee can be assured that the service is committed to securing our borders and taking strong, resolute and urgent action to deal with those amongst us who have not upheld the required standards."

A two-year investigation revealed a cell of corrupt Customs officers allegedly helped smuggle drugs through Sydney Airport - Australia's largest terminal. It prompted the Government to announce a "root-and-branch" overhaul of the agency.

Mr Pezzullo says Customs has been alert to the risks of criminal infiltration for a number of years and has taken steps to guard against it.

Customs has been granted extra powers to weed out corruption, including mandatory drug and alcohol testing, and new powers for the CEO to sack staff because of serious misconduct.

"I am fully committed in my role as acting CEO to use these powers to their fullest extent to harden our service against the threat of criminal infiltration and corruption," Mr Pezzullo said.

He has also flagged a crack down on unauthorised absenteeism, the negligent performance of duties, and poor appearance and presentation, describing them as the "breeding ground for potential serious misconduct and corruption".