A desperate effort to staff the phones after an embarrassing audit report helped Centrelink reduce its wait-time average the next day to less than five minutes per call.

But evidence is emerging that other services suffered as up to 500 officials were redirected from other duties to take calls in a massive damage control exercise after Wednesday's revelations about Centrelink's failing customer service systems.

The main public sector union says Centrelink clients will face delays of months getting their payments approved as officials scramble to catch up on the lost working hours.

But the giant Department of Human Services, which runs the welfare agency, said it had conducted business as usual in the wake of a scathing Auditor-General's report revealing tens of millions of phone calls going unanswered each year.

Callers to the agency's lines were pleasantly surprised on Thursday to find themselves put through, often to a human operator, in what was understood to be less than five minutes on average across the network.

The official "average wait" time published by the Department of Human Services, which runs Centrelink was just under 17 minutes in 2013-2014.

Read how former staff are reacting

The Auditor-General's report that sparked this week's furore was critical of the reporting methods, finding the official version was far removed from the experience of many frustrated callers.

There were few such issues on Thursday as hundreds of officials were taken off other duties and directed to operate telephones with a senior manager admitting frankly in an internal email that the move was a reaction to "significant media attention surrounding our wait times for customers".

But services elsewhere were not business as usual, with clients at the Centrelink office suburban Melbourne, being told by a notice that things might be a little slow that day with staff members unavailable help them with their cases.

Clients were instead encouraged to log onto the internet for a faster service.

Centrelink was already struggling to meet its targets for making decisions on payments, according to the latest official figures.

Just over half of Family Tax Benefit claims were processed within the hoped-for five weeks and only 63 per cent of baby bonus cases decided within the target of three weeks.

But a departmental spokeswoman denied any changes to Centrelink's front desk arrangements to supply workers to the phone-answering effort.

"Staff arrangements in our service centres are managed separately to our call centres and there were no changes yesterday to our face-to-face staffing arrangements," she said.

"The average wait time in service centres yesterday was well within standard."

The DHS spokeswoman also said that it was normal for the department to move workers from processing claims to answering phones and back again.

"Smart Centres have been designed specifically to increase flexibility in moving staff between call and processing work, according to changing demands and priorities," she said.

"These staffing movements have continued this week in line with usual business practice.

"The department regularly uses overtime to keep on top of processing and this will continue to be the case."

Community and Public Sector Union national secretary Nadine Flood said she did not believe the department's claims of business as usual.

"We know this will cause major delays in approving payments and they do not have enough staff to catch up with that work," she said.

"We could see delays of months in approving payments as they struggle to get on top of this backlog."