An angry group of homeless people has gatecrashed the Vinnies CEO Sleepout event being held in Adelaide's CBD, accusing participants of not understanding their plight.

The annual event, held Australia-wide, sees business executives sleep outside in a bid to raise money for homeless services and awareness of homeless people's situation.

Marquees and fences were erected specifically for the event in Whitmore Square, which is usually frequented by homeless people.

St Vincent de Paul chief executive officer David Wark told 891 ABC Adelaide he thought the marquees and fences may have offended the group of five or six people.

"We didn't put the marquees or the fencing in an area where they might normally occupy," Mr Wark said.

"I think it was just having marquees in Whitmore Square was something very different and took people by surprise."

Mr Wark said the homeless people accused participants of not understanding what homelessness felt like.

"The homeless people were demanding in one instance, 'can you give us some money', and in other instances 'what are you doing here? Don't think you know what homelessness is like because you're sleeping out for a night', which is a very fair point to make," Mr Wark said.

"They certainly stayed and made their presence felt and then occupied a seat or two for maybe 15 or 20 minutes, but that's okay, that's a real experience and that's what we're trying to provide people that are doing it.

"There was no doubt it was confronting, but that was the intention of having it at Whitmore Square."

Last night's event, in which more than 120 CEOs took part, raised $560,000 for St Vincent de Paul.

Mr Wark said the money would be used to invest in technology to better service the homeless, as well as being put towards programs aimed at women in crisis.

He said it was hard to measure the number of homeless people living in Adelaide, but demand for meal services had increased over the past year.

"Measuring those that are sleeping rough is a real challenge ... but what I can tell you is Vinnies provides meals through our Fred Van's service and last calendar year we did just over 30,000 and this year we're tracking towards 40,000," Mr Wark said.

"The demand on those sorts of services is certainly most apparent."