SYDNEY - Some offshore creditors of China Evergrande Group are planning to join a winding-up court petition filed against the cash-strapped developer if it doesn't submit a new debt revamp plan by next month, two sources familiar with the matter said.

Evergrande's offshore debt restructuring plan, unveiled in March, has been thrown into uncertainty after the developer said on Sunday that it was unable to issue new debt due to an ongoing investigation into its main unit in China.

The embattled developer has been seeking creditors' approval for its proposals to restructure offshore debt worth $31.7 billion which includes bonds, collateral, and repurchase obligations.

Under the plan, Evergrande, the poster child of China's property sector crisis, had proposed various options to offshore creditors, including swapping some of their debt holdings into new bonds with maturities of 10 to 12 years.

A group of Evergrande bondholders were surprised by the firm's weekend announcement which said it was unable to issue new notes, and have been seeking meetings with the developer to seek more information, said the two sources.

If Evergrande fails to submit a new debt restructuring plan by Oct. 30, that bondholders' group will support a winding-up petition already filed against the developer, said the sources, declining to be named due to the sensitivity of the matter.

The number of creditors who are considering the move and the size of their holdings of Evergrande bonds were not known.

Top Shine Global, an investor in Evergrande unit Fangchebao, in June 2022 filed a winding-up petition in Hong Kong because it said the developer had not honoured an agreement to repurchase shares the investor bought in the unit.

In July, the hearing for that winding-up petition against Evergrande was adjourned to Oct. 30, in order to wait for the result from the developer's meeting with creditors to vote on its debt restructuring plan.

That meeting is scheduled for mid-October. However, the latest disclosure by Evergrande puts the meeting, as well as its outcome, in doubt and it's not clear if the meeting with offshore creditors will go ahead as planned.

Evergrande did not immediately respond to Reuters request for comment.

(Reporting by Scott Murdoch; aditional reporting by Donny Kwok in Hong Kong; Editing by Sumeet Chatterjee and Kim Coghill)