Television New Zealand is investigating an allegation that staff smoked cannabis while in Waitangi during a visit by drug law reform campaigners.

A report on a journey to the Waitangi Day celebrations by activist Dakta Green and others in the "Cannabus" bus featured on Close Up last Tuesday.

Mr Green is a leading member of the National Organisation for the Reform of Marijuana Laws (Norml).

The report featured scenes of drug-taking.

The Herald understands a complaint about the item included an allegation that four TVNZ staff took drugs with the Norml contingent in the bus after filming had finished for the day.

The complainant said the group had photos of the staff smoking the cannabis.

Last night, TVNZ spokeswoman Megan Richards would not give any details of the "serious allegations" or say how many staff were involved, but confirmed that an investigation was under way.

Dakta Green said "some things happened on the trip which are still being sorted out".

He said he was aware of two complaints from Norml members to TVNZ and the Broadcasting Standards Authority, both of which he said related to the content of the Close Up report.

The item was broadcast on the same night as former All Black Robin Brooke appeared on the show to apologise over his behaviour at a party in Fiji early on New Year's Day. The Prime Minister was bumped from Close Up to make way for the Brooke interview.