By Amanda Lee and Ying Xian Wong

Lingering concerns, including over Indonesia's fiscal trajectory and policy uncertainty, are continuing to spook investors, sending stocks and the rupiah tumbling Thursday.

The Jakarta Composite Index fell as much as 5.0% to 5644.23, taking year-to-date losses to 34% and making it the worst-performing market across the region. The currency is the worst performer in Asia, hitting another record low against the dollar at 18,030 rupiah.

The losses extend a recent selloff in Indonesian assets as investors fret over policy uncertainty and market credibility, analysts say.

Indonesian authorities on Wednesday arrested Dadan Hindayana, the recently dismissed head of an agency responsible for President Prabowo Subianto's flagship free-meals program, said UOB Global Economics & Markets Research in a note. The program has been under scrutiny amid concerns that it could pressure central government spending.