Emergency services were called earlier after reports two men were in the water at the mouth of the Wear, near to the Old Pier, Sunderland Yacht Club.
It is believed they went into the water to swim and got in to difficulty, police said.
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One of the men has been rescued, along with two 17-year-old women.
A sea search is under way for a 17-year-old after three teenagers were rescued after jumping off a dinghy off the North East coast.