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Underground operations have shutdown at Cadia East mine, with a blocked vent rise resulting in workforce evacuations on Friday, July 22.

The Central Western Daily understands vent instability has been classed as an inrush and air blast hazard, with underground worker access to the area not permitted until further notice.

The eastern mine, which has a rise that is 900 metres deep, filled with a reported 160 metres of water on Saturday, with the understanding that water levels were continuing to climb.

"Newcrest Mining's Cadia Valley Operations precautionarily evacuated the Cadia East Underground Mine to ensure the health and safety of its workforce," Cadia's general manager, Aaron Brannigan said.

"The mine will remain evacuated and underground operations suspended, until it is determined to be safe for the workforce to return."

With instability in the single VR14-1 vent rise, it's understood that many fly-in fly-out employees have already returned home.

There's no time frame on how long the block will take to fix and that uncertainty has resulted in changes to staffing operations.

"All personnel were unharmed and many are continuing to work in other areas of the operation to continue contributing to the ongoing running of the site," Mr Brannigan said.

"All surface activities remain operational and there continues to be no impact to production or scheduled maintenance activities at this time."

Personnel going underground at Cadia's eastern ore body - which is one of the world's largest gold deposits - has been paused until further notice.

Mr Brannigan also said that an investigation is currently underway, with regard to the cause of the initial blockage and its prospective future.

"Relevant regulatory authorities have been notified in accordance with our Environmental Protection Licence and project approval," he said.

Hazardous vent blockage stops underground operations at Cadia East Underground Mine | Central Western Daily | Orange, NSW