Scientists have discovered the first evidence that dinosaurs roamed the South Island of New Zealand with 70-million-year-old footprints found in six locations.

They are the first dinosaur footprints found in the country although bones, mostly vertebrae, have been discovered in two North Island locations.

The footprints were found by scientist Greg Browne in the remote Whanganui Inlet in the northwest of Nelson at the top of the South Island.

They are spread over 10 kilometres and in one area there are up to 20 footprints, Browne said.

Browne, a sedimentologist, believes the footprints belonged to sauropods -- plant-eating dinosaurs which were among the largest animals to have lived, growing up to six metres (yards) in length and weighing several tonnes.

He said he carefully considered all possible geological and biological explanations for the features in the rock and was able to rule them out one by one.

His investigation included comparisons with dinosaur footprints in similar-aged rocks in other parts of the world.

The footprints were made in beach sands and were probably quickly covered and preserved by mud from subsequent tides.

"What makes this discovery special is the unique preservation of the footprints in an environment where they could easily have been destroyed by waves, tides, or wind," Browne said.

As with much of New Zealand, northwest Nelson was largely submerged between 70 and 20 million years ago and the footprints would have been covered by hundreds of metres of marine sediments.

However, after the country was uplifted and northwest Nelson emerged from the sea, the overlying sedimentary rock has been eroded away over the past 20 million years to expose the footprints again, Browne said.