On Tuesday, Marc Ellis became a multimillionaire but last night he was sleeping rough.

The former All Black was among dozens of business people, community leaders and well-known Kiwis who were part of the Big Sleepout campaign.

The event, run by community organisation LifeWise, began last year and aims to raise funds and the awareness of homelessness in Auckland.

There were dozens of people, including former Auckland City Mayor Dick Hubbard and former Waitakere City Mayor Bob Harvey, many decked out in thick Kathmandu jackets and armed with sleeping bags.

Mr Harvey was seen testing out his spot, lying down on a seat in a corner, and saying: "It's quite comfortable, actually, it's good!"

Everyone got their gear, which included a cardboard mattress with their name and a water bottle, and found a spot in the Auckland University of Technology city campus quad.

Mr Ellis, decked out in a large hooded jacket and with boots, looked warm but was somewhat worried about where he was going to put his cardboard mattress for the night.

"You had to be here early to get one of the good spots," he said, looking over at the sheltered area.

This week he pocketed a $18 million from an overseas takeover deal of his juice company, Charlie's.

Asked if he was worried anyone would ask him for a loan, he laughed. "It's been a good week. But it's not exactly my favourite topic of conversation."

Mr Ellis, who also took part in the Big Sleepout campaign last year, said he had always been a huge supporter of such events, having worked at the City Mission years ago.

"I'm just very fortunate to have met some of the guys there and I think it's a really worthy cause. [Homelessness] is something that's real and I just want to help get rid of it. And particularly girls. There are a lot of young girls out there and it's not good."

Mr Ellis said he felt that local government goals to be rid of homelessness by 2020 were realistic.