Australian Information Commissioner Angelene Falk told Senate estimates on Thursday there were more than 1000 applications for information commissioner reviews of FOI decisions last financial year - an increase of 15 per cent.

There had been more than a 100 per cent increase in the number of reviews coming to her office in the past five years.

There was also a growing backlog of older cases. At the end of September there were 479 matters on their books more than one year old. Of those, 161 matters were more than two years old.

During the last estimates, Ms Falk told senators it had 443 matters older than one year at hand, while there were 59 matters that were older than two years waiting to be finalised.

While the agency had improved its FOI finalisation rates by around 83 per cent, Ms Falk it was "an area of concern".

"We focused last financial year on resolving some of the older measures and ... we improved our finalisation rate by 26 per cent," she said.

"But notwithstanding that with the volume of matters that we are handling, we are unable, unfortunately to to fully keep on top of our 12 month benchmark of 80 per cent resolved within that timeframe.

"There does remain a gap between the volume of work coming into the office and that which we can finalise"

During the last estimates period, the commissioner estimated she would need nine extra freedom of information officers to deal with the volume of requests. Those resources were not provided during this month's budget.

Nearly 300 of the reviews last financial year were linked to freedom of information requests to the Department of Home Affairs.

The information commissioner launched an investigation into the department's failure to process freedom of information requests within the statutory time limits nearly a year ago to the day.

Ms Falk confirmed that investigation was still ongoing.

She said she had hoped to finalise the investigation before the end of the last financial year, but now it would likely be handed down before the end of this calendar year.

The commissioner did get extra resources to deal with the growing backlog of privacy complaints.

"To give you a sense of that work, we had over 1400 matters on hand at the end of the previous financial year, at the end of June 2019. And the end of the most recent financial year, that has dropped to 785 matters on hand. And the previous 12 months, we also had more than 300 matters awaiting allocation. We now in essence, have very few matters awaiting allocation that it ranges on a daily basis but at present, we have around 79. So that's been very pleasing," Ms Falk said.

"We've also had the opportunity to start to increase our enforcement capabilities for investigations on my own initiative. And that includes our intelligence gathering capabilities. I'd say that the last 12 months has really been seeding that capability and we're continuing to build on that over the next two years, based on the funding that's been provided."