Police were alerted just before 10am today.
"Several nearby boaties responded without hesitation, helping to recover seven people from the water," the Coastguard said in a statement.
Six people were pulled out of the water and treated by ambulance staff.
Coastguard volunteers from Waiuku, Papakura, and Auckland and the Coastguard Air Patrol took part in the rescue.
"Volunteers from Coastguard Waiuku met the assisting vessels at Little Huia to provide first aid and check the wellbeing of those rescued," they said.
Coastguard Auckland Air Patrol searched the South Channel for the overturned boat, while Coastguard Papakura checked the front of the bar.
The vessel is believed to have sunk and could not be located.
"As bars like the Manukau Bar can be unpredictable and dangerous, we encourage all boaties to refresh their knowledge by attending one of our Bar Awareness seminars, held across the country and online," the Coastguard said.
