People caught smuggling drugs into Christchurch men's prison will be banned from visiting for up to a year, authorities have warned after three more busts this week.

Prison manager John Roper said a woman was caught on Tuesday with cannabis in her bra, while yesterday a man was caught with cannabis in his underwear.

Also yesterday, another visitor was detained after a package was found concealed in the gatehouse toilet.

"These visitors were found out by a combination of staff vigilance and the ever present prison drug dogs," Mr Roper said.

All were arrested after police were called.

Last month a young boy was used as a drug courier by a woman visiting the prison.

Cannabis oil and items which appeared to be methamphetamine and pills were found and the woman was arrested.

Mr Roper said all visitors to the prison would be closely scrutinised for concealed drugs in the future, and arrested if found to be breaking the law.

"Not only that, you will be banned from visiting the prison for up to 12 months."

Mr Roper said statistics showed drug monitoring was being carried out effectively and warned visitors it was not worth attempting to bring drugs in.

- NZPA