The Department of Internal Affairs neglected to include the entire month of June while calculating ministerial expenses for the last quarter, delaying their public release.

Nearly two weeks ago, the Department of Internal Affairs (DIA) issued a statement saying the travel and accommodation expenses of ministers for the June quarter would be delayed due to a "process error" that occurred during collation.

The expenses are usually released at the same time the Parliamentary Service releases the same figures for all other MPs.

However, MPs' expenses for travel and accommodation were publicly released on August 16, and a week later DIA said expenses for ministers, including Prime Minister Jacinda Ardern, would be further delayed after an oversight was noticed during a "quality assurance, pre-publication verification process".

The Herald has been told that oversight was the omission of ministers' expenses for the entire month of June.

DIA yesterday refused to comment on the error but Prime Minister Jacinda Ardern expressed her frustration over the delay in releasing the information.

"Yes, I am frustrated by that. Everyone's obviously waiting, and it was incomplete information," she told reporters.

Minister responsible for Ministerial Services Chris Hipkins said he was also frustrated and the Government expected better.

"I have asked for a detailed report on how the error occurred and to outline what steps will be put in place to stop this happening again," he said last week.