Regional units are already reeling from expectations of a hike in US interest rates later this year, which analysts say could trigger an outflow of capital from emerging markets to seek higher returns.
China's keenly watched Purchasing Managers' Index (PMI) for factory activity in September fell to its lowest level since March 2009, the latest round of weak data following disappointing readings including on trade, investment and consumer spending.
"The decline indicates the nation's manufacturing industry has reached a crucial stage in the structural transformation process," He Fan, chief economist at Caixin Insight Group said in a statement accompanying the PMI figures.
Dutch bank ABM Amro said the weak PMI reignited "market worries that the slowdown in China may be more pronounced".
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As the world's second biggest economy, China is a key engine for global economic growth and any sign of weakness there impacts on world markets.
The Australian dollar, which is heavily reliant on resources exports to China, tumbled 0.76 per cent Wednesday, while other emerging units also suffered in a flight to safety.
Indonesia's rupiah fell 0.57 per cent to a 17-year low, with research firm Capital Economics saying the country's foreign exchange reserves have plunged 7.0 per cent since March, indicating the central bank had been intervening to support the currency.
The Thai baht and Singapore dollar were also lower
The Japanese yen -- considered one of the safest investments in times of crisis -- advanced against the dollar and the euro. The dollar bought 119.80 yen compared with 120.14 yen in New York Tuesday, while the euro was at 133.41 yen against 133.74 yen.
Expectations of a US rate hike increased this week after three Federal Reserve presidents said they expect to see a lift-off by the year's end.