Two men climbed, then fell off, Cave Rock on Sumner beach in Christchurch on Saturday night.

A man suffered serious injuries after falling up to nine metres off a beachside rock in Christchurch.

He was one of two men who climbed Cave Rock on Sumner beach late on Saturday night.

Police said the men fell between three and nine metres off the rock about 11.30pm.

St John took one to Christchurch Hospital with serious injuries. The other was unhurt.