They included a local police officer, Senior Constable Tim Murdock from Mangonui station, who jumped into the water in his uniform.
Four more children were rescued but did not need hospital treatment.
The drowning occurred at the normally sheltered Cable Bay, near Mangonui in Doubtless Bay, just after 4pm on Tuesday.
Mr Murdock said the children, all siblings or cousins, were caught in a rip at the western end of Cable Bay, opposite Stratford Drive, and swept out past the rocks.
Mr Murdock said Cable Bay was not usually regarded as dangerous but on Tuesday the water was choppy with a strong onshore wind and a rip running at the western end.
He urged people to be aware of the conditions and make sure kids didn't get out of their depth.
Mr Murdock thanked everyone who responded to the man's calls for help and took part in the rescue. He was due to meet some of them yesterday to collect witness statements and thank them in person.
Two crews from Mangonui Fire Brigade responded with chief Antony Pedersen saying firefighters and St John medics performed CPR on the man for more than 30 minutes to no avail.
The 11-year-old girl was unresponsive but still breathing so was given oxygen and placed in the recovery position, then flown to Whangarei Hospital by the Northland Rescue Helicopter.
Rescue helicopter pilot Peter Davies said the initial call was for people in the water so a water rescue team was dispatched in a chopper equipped with a winch.
The first helicopter was still on its way when a second call stated the swimmers had been pulled from the water but another chopper might be needed to transport them to hospital.
The helicopters landed on a nearby rugby field and flew the 11-year-old to Whangarei Hospital in a serious condition. She was initially admitted to intensive care but was yesterday in a serious but stable condition in a regular ward.
Mr Davies said the local policeman ''did a sterling job''.
St John Northland manager Wally Mitchell said another four children were assessed and treated at the scene by ambulance officers from Kaitaia and Doubtless Bay. They did not require hospital treatment.
It is understood the father and children were holidaying in Northland while the mother was still in Palmerston North. The children are now being looked after by the mother and other relatives.
Police will release the drowned man's name once all family members have been contacted.