The friendly mammals were spotted by Conservation Department marine ranger Callum Lilley near the Tapuae Marine Reserve at about 8am yesterday.
Mr Lilley said he initially saw a couple of splashes and thought it may have been the blow from a whale. There have been several orca sightings in the area recently.
Last week orcas were spotted off Stent Rd, Bell Block, Waitara and Mokau as they hunted for stingray close to the shore.
"We went over to investigate and as we approached, the water came alive with dolphins. There were literally hundreds of them, if not over a thousand," he said.
Mr Lilley said at present there were large numbers of schooling fish off the coast and birds and dolphins were right amongst these boil-ups.
"The dolphins looked to be working together herding kahawai."
Mr Lilley said he saw schools of between 20 and 50 dolphins a couple of times a year but it was very uncommon to witness a group of about a thousand at one time.
"Although it is not unusual to see common dolphins off the coast, it was certainly a treat to witness so many involved in a mass feeding frenzy.
"There were large numbers in every direction you looked," he said.