The Department of Human Services told Senate estimates on Thursday that between July 1 last year and March 31 this year, 36.3 million calls had been met with a busy signal, down from 37.4 million calls in the same time period 12 months earlier.

Departmental secretary Renee Leon told senators that the number of busy signals had dropped significantly in the 2018 calendar year. Between October 2016 and March 2017, Centrelink recorded 28.7 million busy signals, while between October 2017 and March 2018, that number was down to 18.1 million.

"We don't consider that mission accomplished, obviously we are going to continue to drive that down," Ms Leon said. The department didn't have a target for reducing the number of busy signals, and wouldn't commit to introducing one, the committee heard.

The committee also heard that the average waiting time on calls had increased between March 2017 and March this year, from 15 minutes and 44 seconds up to 15 minutes and 56 seconds.

In that period the agency recorded 23.379 million "successful calls", which includes both calls that are resolved using the interactive voice recording feature or by speaking to a Centrelink staff member. Of the successful calls, 14 million were classed as "answered," which is defined as speaking to a staff member. Four million calls were classed as abandoned.

Earlier on Thursday it was reported that the department expects the number of busy signals to be around 45 million by the end of the financial year, 10 million fewer than the year before.

Ms Leon told senators that she expected both the number of busy signals and waiting times to decrease as the department implemented recommendations from the Cleveland Report, which was the result of a $430,000 consultation with American consultant Brad Cleveland.

Labor spokeswoman for human services Linda Burney said the increase in wait times was due to staff cuts at the department.

“Malcolm Turnbull has axed 1,280 jobs from the Department of Human Services which will make it more difficult to contact and access Centrelink," Ms Burney said.

“The truth is Centrelink is understaffed and under-resourced. Centrelink needs permanent, full-time staff who are properly supported and equipped to manage the complex issues facing income support recipients.”

Greens spokesperson for family and community services Rachel Siewert welcomed the reduction in busy signals, but said the wait times were too high.

"I welcome the busy signals to Centrelink finally starting to drop after increasing exponentially. At the end of those busy signals were exasperated members of the community trying to get through for support. Let’s be clear, there are still 36,360,094 busy signals this year to date," Ms Siewert said.

"In addition wait times are still too long. People should not be waiting on average over 15 minutes for someone to answer. The wait times on some lines are over half an hour, across the board that is just too high and on some lines those call wait times have actually increased."

Community and Public Sector Union national secretary Nadine Flood said busy signals had "absolutely ballooned" in the past four years.

“Four years ago the figure was 22 million and that had rapidly grown to 55 million last year. Why did it take so many years for the Government to realise this was a problem?”