Inland Revenue had yet to confirm it had a problem as of late on Tuesday afternoon.

Accountants are complaining they are facing big problems logging on to Inland Revenue's MyIR tax system, with one saying the department appeared to be in a state of crisis.

John Cuthbertson, New Zealand tax leader at Chartered Accountants Australia and New Zealand, said it was aware from a number of sources of widespread problems.

"The issue came up at our national tax liaison meeting last week. We have had accountants call in to us and have logged the issue with Inland Revenue and followed up again today, but haven't yet had a response."

IRD took down its online service for four days in April, but accountants say they are now experiencing unexpected problems logging on.

"There have been issues with either slowness or getting on, online. It varies between being very slow to pages breaking up when you go online to look at things."

READ MORE

* More than 4000 public servants at MBIE and IRD vote to strike

* 'Your call can't be connected due to high demand'

* Inland Revenue has foot on two stepping stones

Cuthbertson said the problem was serious "in the sense that it is causing delay".

"I'm not sure it is locking people out completely."

Wellington accountant Matthew Underwood, who runs his own chartered accountancy firm Matthew Underwood Ltd, said clients were struggling to file GST returns and he believed the integrity of the whole tax system was under threat.

"We can't log in; it is telling us that our password and usernames aren't right. Though occasionally it will let us log in using the same credentials.

"Sometimes when you do get in, all my staff will see is a massive logo. It is totally random. Our clients are having the same problems."

Underwood said he personally had not been able to get into MyIR at all for weeks.

The issues meant accountants might have no idea where someone was with their tax, he said. "Has someone paid their provisional tax? Maybe. Total sensory deprivation."

Underwood said he had written to Revenue Minister Stuart Nash, Inland Revenue commissioner Naomi Ferguson and Finance Minister Grant Robertson to alert them of the problems.

Inland Revenue has faced separate complaints about long delays reaching it by telephone, with many callers over the past two weeks being greeted with a recorded message telling them to call back later.

The tax department blamed that on it being a busy time of year.

But Cuthbertson said Inland Revenue's MyIR online system shouldn't be struggling under a seasonal workload.

"It shouldn't be high usage causing the problem because it should be designed to handle that."

Combined with the difficulties reaching Inland Revenue by phone, the problems with the online system were creating "a perfect storm", he said.

Cuthbertson said Inland Revenue was "definitely aware of the issue".

Inland Revenue repeatedly declined to confirm it was in fact aware of a problem when contacted by Stuff on Tuesday afternoon, with a spokesman saying it would prepare a statement.

The Public Services Association union described Inland Revenue's technology projects as "a mess" earlier this week, and said that was having a major impact on staff.

National secretary Erin Polaczuk said Inland Revenue's systems were not equipped to process the best start tax credit payments, due to start next week, that should give lower income families an extra $60 a week for each child.

That meant the payments would have to be processed manually, drastically increasing their workload," he said.