The rescue of two visitors stranded by the high tide while fishing off rocks has prompted a police warning for people to keep a close eye on sea conditions.

A 36-year-old man and a 27-year-old woman, both from Auckland, struck trouble about 6.30pm on Sunday while fishing off rocks at the northern end of Langs' Beach near Waipu.

With the waves crashing on to the rocks they used their cellphone to call 111 and two fire appliances from Waipu went to the rescue.

Waipu deputy fire chief Alan Vaile said the duo had climbed onto the rocks to go fishing at low tide and did not realise they would be stranded by the in-coming tide.

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They were on the wrong side of a 3 metre wide gut in the rocks. When the tide came in it made it impossible for the fishers to get back safely.

"We used a ladder across both rocks and a rescue line and successfully got them across.

They were not injured but were very cold from the rough conditions at sea," Mr Vaile said.

He said his firefighters have previously rescued people from rocks on that stretch of coastline but not from the spot they went to on Sunday.

Police from Maungaturoto spoke to the Aucklanders after the rescue.

Waipu police Senior Constable Martin Geddes called on people to have "commonsense", especially when sea conditions were rough. When rock fishing, people should know what the tides are like and to keep a close eye especially on the incoming tide. They probably didn't even know about the tides before going out," Mr Geddes said.

Police search and rescue incident controller Constable Jim Adamson said people who were ill prepared before venturing out to sea could quickly find themselves in trouble.

"These two had formal communications' equipment which was good. People should also have lifejackets on but our usual advice is around being better prepared, especially if you're unfamiliar with the area," he said.

He said sea conditions were quite rough on Sunday and had the two fallen into the water, they would have been badly bashed against the rocks.