Visitors are being urged again to avoid the iconic Cathedral Cove on the Coromandel Peninsula after a third rock fall in just over 12 months.

Department of Conservation (DOC) Hauraki area manager Melissa King-Howell said the latest rock fall, noticed on Thursday, was the biggest so far.

"This latest rock fall shows that the danger is very real and someone will get injured if they continue to put themselves at risk," Ms King-Howell told the Waikato Times.

A large section fell from inside the arch in the latest fall, which Ms King-Howell said showed stability was worse than they previously knew.

The arch has been closed to walkers for 13 months as public safety was of paramount concern.