Orica says it is producing ammonium nitrate at its Newcastle plant again after being allowed to restart some of its facilities last week.

The chemical company was cleared to restart three nitric acid plants and two ammonium nitrate plants on the Kooragang Island site after the lifting of a prevention notice issued after a leak in November.

Orica said on Tuesday ammonium nitrate production had now resumed, and the restart of remaining ammonium nitrate production facilities were progressing.

The ammonia plant at Kooragang Island remains closed subject to the lifting of another prevention notice issued in August after a leak of hexavalent chromium.

Testing on the plant is continuing, Orica said.