More than 200 participants and vehicles, which range from small one-tonne trucks to the full-sized multiwheelers which ply the nation's highways every day, are taking part in the tour.
Trucks range from the 1930s to the 1990s and remain either in original condition, or have had tens of thousands of dollars invested in their restoration.
The convoy left Picton for Timaru on Monday and was southbound via the West Coast, Central Otago and Southland, before returning to Timaru.
Tour spokesman Simon Vincent, of Timaru, said this week the classic and vintage truck movement had grown throughout the country as those associated with the transport industry realised the value of preserving its history.
"This year will witness the third interisland classic truck run and this year's event will be the largest so far," Mr Vincent said.
"It has been five years since the first major truck run travelled around the South Island."
Interest in the event was so strong it attracted entries from Australian enthusiasts who shipped their trucks over especially to take part, he said.
The tour will travel from Twizel to Queenstown today, with time set aside for attractions and activities, then move on from the resort to Te Anau on Saturday and Te Anau to Milford on Sunday.
"The best place for [Wakatipu] people to catch up with us will be at the Cardrona Hotel today around 1.30pm to 2pm. We will also be around the Wanaka Airport area during the morning," Mr Vincent said.
"The evening we are in Queenstown is free and tour members will be staying all over town with some in Cromwell. We are departing for Kingston the following day."
