World Rugby chairman Bernard Lapasset said Lomu was a giant whose contribution to rugby “cannot be overstated”.
A private family burial service will be held in Auckland on Tuesday for Lomu, who died on November 18.
Many of the mourners at Auckland’s Eden Park were wearing Lomu’s No 11 shirt.
Mr Lapasset, who flew to New Zealand from France, joined New Zealand prime minister John Key and former All Blacks teammates in paying tribute to Lomu’s contribution to rugby and his charity work.
Lapasset described Lomu as “a giant of a man (who) leaves a giant space in world rugby - he will forever be a big part of rugby’s story”.
Mr Key recorded a video tribute in Paris, where he is attending the world climate conference, saying Lomu made a real difference in people’s lives.
“He proved that you can come from anywhere in New Zealand in any background and make it to the top,” Mr Key said.
One of the most moving tributes came from pupils of Lomu’s former school, Favona Primary in South Auckland, who wrote and performed a tribute song.
The pupils sang of Lomu as “No 11, our friend in heaven”.
The memorial opened with a traditional haka and powhiri, or welcome, performed by indigenous Maori representatives of Auckland’s Ngati Whatua people.
Lomu’s coffin was then borne into the stadium by pallbearers including former All Blacks Michael Jones, Frank Bunce, Joeli Vidiri and Jerome Kaino, as well as New Zealand rugby league player Manu Vatuvei.
The coffin was followed by Lomu’s wife Nadene, who wore a woven skirt which is a traditional Tongan symbol of respect and mourning, and by Lomu’s sons Brayley, six, and Dhyreille, five.
Mourners watched a video montage of high points in Lomu’s rugby career, including a tribute paid to him by British singer Sir Elton John during his recent concert tour to New Zealand.
Former All Blacks coach John Hart spoke on behalf of Lomu’s wife and children, thanking mourners and expressing gratitude for the tributes that had poured in from around the world.
Mr Hart recounted Lomu’s almost 20-year battle with the debilitating kidney illness nephrotic syndrome which eventually forced his retirement and is thought to have contributed to his death.
Lomu first became aware of the illness in 1995, but kept it secret from the public and from teammates until he was forced to undergo regular dialysis treatments.
Mr Hart said Lomu’s illness meant he played all of his career at only 80% capacity.
“It’s frightening to think what he could have done on the field had he not played with such a huge medical handbrake,” he said.
“He overcame tremendous hurdles throughout his life but never, ever complained. He was a fighter until the very end.”
Lomu, who underwent a kidney transplant in 2004, played 63 tests for New Zealand and Mr Hart described him as rugby’s “first superstar” who “left his huge footprint around the world”.