HONG KONG (Reuters) - A group of major bondholders of defaulted Chinese developer Shimao Group ( SIOPF ) said on Wednesday it "firmly opposes" the firm's proposal to revamp $11.5 billion of offshore debt, clouding its prospects amid a deepening crisis in the property sector.

"The ad hoc creditor group firmly opposes Shimao's ( SIOPF ) restructuring proposal, (and) will unequivocally vote against it and other scheme creditors ought to do the same," the offshore creditor group's financial adviser Houlihan Lokey ( HLI ) said in a statement.

The group did not cite any reason for the opposition, but three Shimao ( SIOPF ) creditors told Reuters they were not happy about the steep haircut in the proposal, as well as a lack of upfront payments and cash payments in the next four to six years.

Shimao ( SIOPF ), which defaulted on its offshore debt in 2022 after an unprecedented liquidity crisis hit the sector in mid-2021, on Monday laid out detailed restructuring terms to revamp its offshore debt with an aim to cut its debt by 60%.

Shimao ( SIOPF ) would require approval from more than 75% in creditor value to pass its restructuring proposal. The ad-hoc bondholder group holds more than 25% of Shimao's ( SIOPF ) outstanding $6.8 billion dollar bonds.

A separate bank creditor group, advised by Deloitte, holds around $4.7 billion of loans.

A source close to the bank group said the group was also not happy with the latest terms, which they think give worse treatment to the group than when they first started negotiation in 2022.

Shimao ( SIOPF ) and Deloitte did not immediately respond to request for comment.

Separately, Deutsche Bank is preparing a liquidation lawsuit in Hong Kong against Shimao ( SIOPF ), Reuters reported early this month.

Creditors in both the bondholder and bank groups said after Shimao's ( SIOPF ) proposal this week that a winding-up petition could be useful to the negotiation process.

Shimao's ( SIOPF ) creditors would receive a total of 1.1% consent fee based on the outstanding principal of their debts if they agreed to support the restructuring by end of April, and 0.6% by end of May.

(Editing by Sumeet Chatterjee and Kim Coghill)