Another woman jumped into the water to help.
"We saw these kids yelling out for help so that's when I jumped in the water to help. I've got three kids myself so I understand," the woman said.
As the family were swept westward by the current, some of them managed to grab the pylons under the old Mangere bridge next to the motorway bridge, said Senior Sergeant Ian Brenchley.
"Two members of the public have jumped into the water to assist them, so that was seven people in the water at one stage and we've recovered five of those. Police search and rescue are searching for the other two bodies," Senior Sergeant Brenchley said.
The secondhand dinghy had only recently been bought by the Mangere family and they were trying it out for the first time, the brother of the man who owned the boat told One News.
The firefighter was treated for suspected mild hypothermia, and then returned to the station.
Water Safety New Zealand CEO Matt Claridge told Newstalk ZB this morning that the Manukau Harbour is renowned as a good fishing spot.
"Like most good fishing spots it has fairly variable conditions. It can be quite risky,'' he said.
"The tide can move really fast and ... can be actually a fairly dangerous environment to be in.''
Children's cries of terror in tragedy
Terrified children clung to one another and screamed, "Help me, help" and "We're cold", after their dinghy capsized as a man, believed to be their father, floated face-down nearby.
Grave fears were held last night for a missing 45-year-old man and a seven-year-old child as rescuers called off a search of the Manukau Harbour in fading light.
Witnesses said the dinghy looked overloaded but police said it was too early to say what caused it to capsize.
Several people scrambled into chilly water near the old Mangere Bridge to help. One man threw a rope to the children and helped drag two of them ashore.
A firefighter who helped in the rescue suffered hypothermia and was taken to hospital.
A fisherman who saw a two-year-old girl float past jumped into the water and supported her until a paramedic was winched down from the Westpac rescue helicopter.
"He suffered some quite bad cuts and gashes for his troubles," a helicopter spokesman said.
"He was just a guy who was watching and he jumped in. If it wasn't for him the kid would have carried on past and would have drowned."
Angela and Gary O'Donnell heard the cries for help. "We told the kids to hang on, keep holding on, don't panic [and said], 'We've got the chopper and police coming'."
The children's pleas for help were terrible to hear. "'Help us, help us.' This is all those poor kids were yelling out. 'Can you help us, can you get us out, we want out and we're cold'," Mrs O'Donnell said.
Some of the children were not wearing life jackets and struggled to stay afloat - using the others for survival.
"You could see them in water," Mrs O'Donnell said. "They tried to hold onto each other to support each other."
One man threw a rope into the water and dived in to help but he could not swim with the children because they were too heavy. He was later taken away by ambulance.
Mr O'Donnell told the Herald two young boys and a man were pulled in by the rope.
Mrs O'Donnell said someone called out directions to where a man was floating face down in the water.
"My husband yelled out, 'Turn yourself over, turn yourself on your back.' It was a real horrible thing to see."
They could see the man's red T-shirt inflated in the water but then lost sight of him.
Utu Togafau, one of the rescuers taken to hospital, said she could not ignore the cries for help and did whatever she could.
"It was a lovely Sunday [until] we heard the kids yelling for help. I've got three kids myself so I understand. I just wanted to get those kids safe, as a mother."
The cold water was moving quickly, which made the rescue even more difficult. Even those in the water a short time were left shivering uncontrollably.
Others had cuts and scratches on their legs from the shells under the bridge.
Onlookers were distraught at seeing young children in distress. One tearful woman was asked if she needed to speak to Victim Support counsellors after what she witnessed.
A Westpac helicopter spokesman said the dinghy was upside-down when the rescuers arrived.
"We saw people standing on the bridge pointing - [the victims] were under the bridge."
A paramedic was lowered to the area and the 2-year-old girl was winched to safety and taken by ambulance to hospital.
Mangere station officer Willie McDonnell said of the firefighter who suffered mild hypothermia: "We let him out on a line because you can't really afford to let anyone go in that current - it was about half tide so it was getting pretty strong."
Mr McDonnell said the situation was "flat out. It was a little bit confused because people didn't know how many people were in the boat. I didn't even see a boat. All we found were the people clinging to the base of the bridge."
Mangere Boat Club commodore Brian Anderson said he saw what looked like an overturned dinghy floating on the outgoing tide past the clubrooms, 600m from the bridge.
It was a small vessel and did not look suitable to carry many people.
Water Safety New Zealand chief executive Matt Claridge said any water-related tragedy was sad. Safety should always be the paramount consideration when people headed out on the water.
"Everyone should be wearing a life jacket - that's the main message. Child, adult, everyone should be wearing one. The skipper is ultimately responsible for this."
The Mangere Bridge area was a popular spot for locals, Mr Claridge said. "It's great for fishing - but where there's plenty of fish, there tends to be dangerous waters."
"It appears as though the dingy was overloaded, lack of preparation in terms of everybody wearing lifejackets, and from what I can gather too much enthusiasm to head out on the water at a time probably wasn't quite right."
Mr Claridge said anyone buying a new boat should have a Coastguard boating education course under their belt.
As of May 9, 45 people had drowned in New Zealand waters. At the same time last year, the toll was 60.
Additional reporting: APNZ, Vaimoana Tapaleao
