Demolition experts are to attempt to remove the internal pressed copper dome of the quake-damaged Catholic Cathedral in Christchurch this afternoon.

The historic Basilica suffered massive damage in the February 22 earthquake, but it is hoped the building can be safely dismantled and reconstructed in the future.

Opus, who are undertaking the work, said the removal of the main dome has been completed and believe the ornate internal dome can also be safely removed.

In an update on the project, Opus said the internal dome has lost some support at the base due to all but six columns collapsing in the February earthquake and is only supported by timber jolts and a thin, damaged cantilever concrete slab at the base.

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"With the risk of further aftershocks still at an elevated level, there is still some risk of further damage to this otherwise intact part of the main dome due to the degrading state of the structure around it," Opus said.

"Given the fact that this dome is a highly decorative part of the building, and is virtually undamaged, we plan to remove this by releasing the timber frame, and enabling the internal dome to be salvaged intact."

The dome will be removed in one piece at 2pm.