China’s property market is bracing for a worsening crisis at state-backed China Vanke Co., as the builder struggles to convince investors it can avoid default in the months ahead without clearer signs of government support.

Once China’s largest developer and now a bellwether for the nation’s struggles to ease broader property woes, Vanke plunged in credit and stock markets this week. The builder’s local notes extended their declines Wednesday, with its bond due in May 2028 dropping as much as 29 yuan to 65 yuan, triggering brief trading halts.