The Brazilian oil company surveying the seabed off East Cape says it will continue in the face of mounting protests.
Petrobras was awarded a permit last year to explore 12,000 square kilometres in the Raukumara Basin for gas and oil.
Greenpeace says the permit should be revoked after a flotilla of boats protested for a week against the company's plans.
Two survey vessels have been in the area since Sunday and Petrobras says a seismic study has begun, in the first phase of a five-year programme.
The company says it respects the rights of protesters to express their views, but it will continue with the commitment it gave the Government.
Petrobras says the first two survey phases will cost $US30 million.