Cracks up to 20 centimetres wide have opened on land in Camberwell Common, delving metres below the surface.

A pole lowered into one of the fractures reached at least three metres, Camberwell Common Trust secretary Deidre Olofsson said.

"How far they really go down, I don't know," she said.

The ravines, which stretch up to 40 metres across the parcel of Crown land, were discovered this week, forcing the trust to cordon off the area to prevent injury to people or livestock.

"There's at least eight cracks," Mrs Olofsson said.

"And the grass is so long there that you can't tell if there are any more running down the hill. They could be really dangerous."

The trust fears the ground ruptures could cause a landslide and do major damage to neighbouring Glennies Creek.

Blasts from nearby Ashton mine that shook Camberwell homes every day were to blame, trust president Colin Stapleton said.

"You can see the cracks going straight over into the mine," Mr Stapleton said.

But Brian Flannery, managing director of Felix Resources, which operates the mine, said it had had no adverse effect on the common.

"From what we have seen there is absolutely no problem," Mr Flannery said.

"There are a couple of cracks in the road that goes past our mine, but there is no danger to any village, or any danger of a landslide on that village.

"Surface cracks can be caused from very dry weather. In this case it could have come from blasting, but all it takes is a small excavator to run over and fill them in with fine material and they won't propagate any further."

Mr Flannery said geologists had inspected the grounds regularly and no problems were reported.

The Department of Planning has launched an investigation into the Camberwell cracks.