Under international accounting rules, unless a company holds a controlling interest in a joint venture, it can keep details of a joint venture and the debt it takes on off its balance sheet - recording instead just the amount of equity it has invested in the project.
The practice is raising eyebrows now among investors trying to assess a company's credit risk, as they worry they may have underestimated the scale of developers' off-balance sheet debt just as China's economic growth is slowing.
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"Transparency is like an umbrella, nobody cares about it until it rains," said Victor Yeung, chief investment officer of Hong Kong based Admiral Investment.
"The market is realizing more the disclosure is inadequate.... and this raises the risk premium of the whole sector," he added.
In February, struggling developer Kaisa Group stunned investors when it reported its debt had more than doubled to $10.4 billion (6.91 billion pounds) in just six months. The reasons for the rise are still unclear, though several analysts have suggested borrowings of its joint venture projects could explain part of the jump.
Kaisa, which defaulted on a bond coupon payment on Monday, declined to comment on its joint venture holdings.