Police are hunting for a robber who walked into a Christchurch bank and demanded money this afternoon.

Police were called to the Woolston ANZ Bank about 3.20pm after alarms at the branch were activated, Detective Sergeant Al Lester said.

A man, believed to be in his 20s, entered the bank carrying a bag, presented an "item", and demanded money from a teller.

A small sum of money was handed over before he left the bank.

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The bank teller was not injured.

Police were tonight working with the bank to access security camera footage.

Ms Lester said he would not say what item was presented at the teller for fear of copy-cat acts.

The alleged robber is described as a male Caucasian in his early 20s, tall and of medium to slim build.

He was not disguised and police hoped to get pictures of him by tomorrow.

Police would like to hear from anyone with any information on the robbery.