A search for two 17-year-old boys swept into rough seas off the coast of New Plymouth and the instructor who went to help them will resume on Thursday.

A group of 11 year-13 students from Spotswood College and two instructors got into trouble on Paritutu Rock near Back Beach while out rock climbing on Wednesday afternoon.

Two 17-year-old boys - one from New Plymouth and one from Brazil - were swept into rough seas and an instructor, a New Plymouth man aged in his 40s, jumped into the water to help them.

None of the three resurfaced and they have not been seen since.

A third boy who fell into the sea managed to clamber onto rocks and was winched to safety by the Taranaki Community Rescue Helicopter along with the other students and instructor. They were all taken to Taranaki Base Hospital but have since been discharged.

Searchers on foot, in boats and on board a small plane scoured the water and the coastline on Wednesday evening but extremely rough sea conditions hampered search efforts.

Incident Controller Inspector Frank Grant said just after 9pm on Wednesday that the search had been called off and would resume at first light on Thursday.

"Police remain optimistic but given the rough sea conditions, the weather and the length of time the trio have been in the water, hopes of finding them alive are fading," he said.

The Police National Dive Squad will arrive in New Plymouth on Thursday and may assist with the search. The Royal New Zealand Air Force may also lend a hand.

The names of the missing three are expected to be released on Thursday.