The Department of Industry and Investment has told The Herald its safety inspectorate issued a notice for Ashton Coal to stop mining activities in its highwall slip area to prevent further cracking.

The news comes after reports that more mysterious cracks, up to 20 centimetres wide, had appeared on the parcel of Crown land.

Ashton Coal had recently finished repair work on older land fractures, which stretched up to 40 metres long and was metres below the surface.

Camberwell Common Trust president Colin Stapleton said the continued cracking indicated the common was "clearly unstable".

He said further blasts could cause a landslide, which would devastate Glennies Creek.

"If we get some heavy rain I think that hill could slip," he said.

"There could be a landslide towards the creek, and if it goes into the creek, that's the whole water supply Lower Hunter farmers use for irrigation ruined.

"Thousands of people would be affected."

Felix Resources managing director Brian Flannery said mining in Ashton's highwall section was stopped in December.

He said large areas of the mine had since been backfilled, leaving 270,000 tonnes of coal plus overburden as a buttress.

"From a mining point of view the area is stable," he said.

"Until cattle are removed from grazing the slope near the creek and preventing erosion of the cliff that area will not stabilise."

An Ashton Coal commissioned geotechnical report into the cracks had reported that steep slopes down to Glennies Creek and dispersive soils had caused localised slumping and was not related to mining activity.

The Department of Industry and Investment said the mining ban would "remain in place until Ashton Coal could demonstrate the highwall had been stabilised".

The department's safety inspectorate is reviewing the situation and reports from geotechnical consultants were due soon, a spokeswoman said.

In parliament last week Greens MLC Lee Rhiannon tabled questions for Lands Minister Tony Kelly over subsidence damage in the area and Ashton Coal's actions.

Mr Kelly's response is expected by April 10.