A tobacco retailer in Blenheim has been caught selling cigarettes to an underage volunteer.

The 14-year-old was part of a tobacco controlled purchase operation by the Nelson Marlborough Public Health service last week.

26 retailers in the Nelson, Tasman and Marlborough regions were visited by the volunteer who attempted to buy cigarettes or tobacco from the stores.

Public Health Service manager Peter Burton says while it was pleasing to see no sales made from 25 of the stores, even one sale is a concern as the risk of starting smoking is greatest amongst young people.