Greenpeace has intercepted one of the world's largest seismic blasting ships 50 nautical miles east of Wairarapa.

The ship, the Amazon Warrior, was in the area searching for oil on behalf of Statoil and Chevron.

Campaigner Kate Simcock said she radioed the ship to deliver an open letter signed by more than 60,000 New Zealanders.

A message on behalf of 80 indigenous communities from the East Coast was also delivered, demanding the oil giants cease activities in their customary waters.