The parents of a New Plymouth Prison inmate were busted last week allegedly attempting to smuggle cannabis to their son.

The Corrections Department said the father, who arrived first, became agitated when a prison drug dog handler informed him his vehicle would be searched.

He tried to hide a package containing about 12 grams of cannabis in his pocket but was spotted and asked to hand it over.

Later that day the mother arrived and quickly drew suspicion when she stopped her car halfway to the prison entrance, apparently debating whether to enter the grounds.

The drug dog handler arrived and asked her to get out of the car so it could be searched, the department said.

She tried to palm something and on being asked to hand it over tried to slip it into her pants. She failed and a bag, containing cannabis leaf, fell on the ground.

Police were called in both cases and the parents arrested.

"Parents should be the last people bringing drugs in for their children, but unfortunately this is not the case," prison manager Peter Madsen said.

"We know people come under immense pressure to supply drugs to prisoners but it just isn't worth being arrested over."

Her said that as a result of their action the parents would be banned from visiting their son for six months.