An "embarrassing" administrative blunder by the NSW Independent Planning Commission (IPC) saw a 21-year mining lease approved before public submissions had closed.

Key points: The erroneous announcement was due to an administrative error by the Independent Planning Commission

The erroneous announcement was due to an administrative error by the Independent Planning Commission It meant miners were initially told their jobs would be secure, only to be told hours later a decision had not been made

It meant miners were initially told their jobs would be secure, only to be told hours later a decision had not been made The Government has announced an immediate review into the commission

The decision was published on Friday afternoon and gave the Bloomfield Group the go-ahead to operate the Rix's Creek South Mine near Singleton until 2040.

Just a few hours later, the Commission reversed the approval, saying a decision on the mining lease had not yet been made.

It is understood hundreds of workers at the site were told on Friday their jobs were secure after a six-year wait, only to be told the IPC had withdrawn approval a few hours later.

NSW Minerals Council chief executive Steve Galilee said that left 300 workers devastated.

"They were very relieved when the news came through yesterday afternoon that the project had been approved," he said.

"They now have to wait to see whether they have a long-term future again. It's obviously, personally, a very, very stressful time for 300 people and their families."

'It's very embarrassing'

The commission's chair, Mary O'Kane, said the announcement was the result of human error and had hit the organisation hard.

She said the secretariat allowed nine days for public comment when it should have been seven days.

Professor O'Kane said it was not normal for information granting approval to be written up prior to all submissions being received.

"It's embarrassing for the IPC because we try to work hard to give everyone a chance to comment and give as much input as possible, it's very embarrassing."

The commission learned of its mistake through comments on Twitter and, upon legal advice, reopened the period for comment, which means the public will have a total of 16 days for submissions.

NSW Planning Minister Rob Stokes said he had asked for an immediate review into the commission to ensure a mistake like this was not repeated.

"It may only be a further weeks' delay, but after six years of uncertainty, a week will seem like an eternity to the Upper Hunter community," he said.

Professor O'Kane said she strongly welcomed the review and was "conscious" of the need for significant change in the way the commission operated.

Labor leader in the NSW Upper House Adam Searle said the incident was an example of the chaos hampering the state's planning system.

"This will further undermine community confidence in the rigor and integrity of the system," he said.

He said the Government did not adequately resource the IPC.

"The key problem is that it's still composed of part-time and sessional members," he said.

"When they're not sitting on the IPC, they are selling their goods and services to industry. I think that is an inherent conflict of interest."