Concern has been raised that Brisbane City Council's investment arm could put $270 million of ratepayer funds at risk.

The City of Brisbane Investment Corporation (CBIC) is the Council's future fund, tasked with investing revenue from ratepayers to deliver returns to the city.

But Opposition and independent councillors say CBIC is concentrating its investments too heavily in the property sector, and risks heavy losses in a downturn.

Reports say economic analysts PwC have been commissioned to review CBIC's operations, and that the experts raised concerns about CBIC's investments and practices.

The PwC report has not been made public.

Economist Gene Tunny, principal of Brisbane firm Adept Economics, has echoed the concerns about CBIC's investments.

“What the Council seems to be doing, it's going into very high-risk property investment and it's putting all of its eggs in the one basket,” Mr Tunny told the ABC.

“It's got some capital here and I think the ratepayers of Brisbane would be better off if they put that into a diversified portfolio.

“What the CBIC is doing, it's highly risky.”

Property makes up 55 per cent of CBIC’s total investment mix.

Mr Tunny said “any financial adviser would say [CBIC is] massively overweighted in property”.

“Given that they're investing on behalf of the Brisbane ratepayer, I would say that anyone who looks at that would be suggesting that they diversify,” he said.

“I think we need to have a serious look at whether it makes sense for the Council to be acting as a property investor.”

The economist said CBIC’s latest annual reportsuggested it is buying from council at “much more favourable prices” than private developers would have to pay.

“It appears to be getting preferential access to properties owned by the Council, and it is also benefiting from leasing out space to the Council at many of its investment properties,” he said.

“So part of the return it earns could simply be a transfer of value from the Council to CBIC, as the Council has denied itself the higher prices that private developers may have paid, and CBIC benefits from having secured the properties at very favourable prices.”

The Council has issued a statement saying CBIC's investments have generated significant returns.

“Since its inception in 2008 with net assets of around $135 million, CBIC has more than doubled its net asset base to over $273 million,” it said.

“CBIC's property portfolio has delivered the ratepayers of Brisbane consecutive double-figure investment rate of returns and over the past five years.

“CBIC delivered another record $20 million dividend to ratepayers in 2017 — the equivalent of a 2 per cent rates increase that has been reinvested in frontline council services. Since 2009 a total of $90 million in dividends has been paid to council.”

Mr Tunny said the Council should release the PwC report on CBIC.

The Council’s Labor Opposition recently moved to have the report released, but was voted down 20 to seven.

Opposition Leader Peter Cumming said CBIC's lack of transparency makes it difficult to keep it accountable.

CBIC’s official distance from the local government also means it cannot be held to account by right-to-information requests.

“They're relying on this being a private entity that's divorced from council but it's all ratepayers money we're talking about,” Cr Cumming said.

“They're treating the assets as though it's a private investment company and the Council's not scrutinising them, and if that's the case then ratepayers should be worried about it.”

“It's a recipe for disaster.”

Cr Cumming said he is concerned about a lease between council and CBIC for a property CBIC bought from a council-owned company, which is now rented by Brisbane City Council for $3.5 million a year.

“The Council boasts about the dividends they get from the CBIC but if they're paying them generous rent, it's ratepayer money going to them,” he said.