Data showing little respite for Chinese manufacturers in the world's second-largest economy, also dampened sentiment.
The South Korean won led the slide among regional units as traders scrambled to reduce bullish bets on the unit.
The Indian rupee fell to its lowest in nearly a week as a key ally of the country's ruling coalition withdrew its support, raising worries the government may roll back key reforms such as the increase in diesel prices.
The Malaysian ringgit and the Thai baht also shed on dollar-short covering.
The depreciation came amid growing tensions between China and Japan over a disputed island chain and as other risky assets such as Asian shares extended losses after lackluster Chinese manufacturing data.
A private sector survey on manufacturing activity in the country showed a contraction for the 11th month in a row in September, signaling the economy remains on track for a seventh quarter of slowing growth.
French business activity took a sharp turn for the worse in September, shrinking at its fastest rate since April 2009, a separate poll showed.
Maybank FX research head Saktiandi Supaat in Singapore said a sluggish global economy is likely to prevent investors from continuing to absorb Asian assets.
"The question is whether real money funds are willing to pour in more into this region," said Supaat, adding assets in emerging Asia appeared "pricey" and yields were not high enough to attract more money.
Most emerging Asian currencies have rallied so far this month as the Federal Reserve launched a third round of quantitative easing and European policymakers took steps to ease the continent's debt crisis.
Still, Supaat said regional units were expected to find support as long as investors maintain hopes for more stimulus measures from China.
Some investors scaled back expectations for Beijing's actions with a slight improvement in the HSBC Flash China manufacturing purchasing managers' index (PMI).
But Supaat said there was still a chance China would ease policy, as the pace of the economic slowdown though stabilising, was not very significant.
WON
The won eased as caution grew over possible intervention by the foreign exchange authorities to stem its strength, prompting traders to cover short dollar positions.
The South Korean currency weakened past 1,122.8 per dollar, the 38.2 percent Fibonacci retracement of its appreciation between late August and early September. It may head to the 50 percent retracement of 1,125.7.
Still, investors hesitated to sell the South Korean currency, given foreign investors' continuous purchases of Seoul shares.
Dollar demand from domestic importers also slowed down, dealers said.
"It is difficult to buy the won when it is stronger than 1,115 per dollar. But it is also difficult to expect the won to weaken further, given incoming liquidity," said a South Korean bank dealer in Seoul.
RINGGIT
The ringgit turned softer, weakening past 3.0720 to the greenback, the 38.2 percent retracement of its strengthening between August and September.
The Malaysian currency started the day firmer on some fund inflows.
Technically, the local unit is seen heading to the 50.0 percent retracement line of 3.0835.
PHILIPPINE PESO
The Philippine peso edged lower as traders booked profits as they were wary of potential intervention by the central bank, dealers said.
A European bank dealer in Manila said the peso was expected to weaken further, adding investors still appeared to hold short dollar positions to cover.
"The market is looking for negative news to justify profit-taking as most of the good news has been factored in," the dealer said.
"Dollar/peso has to try to the upside first and shake out short positions before trying to test lower levels."
BAHT
The baht slid as local and foreign banks sold the Thai currency with offers around 30.82 per dollar and 30.83.
But traders expected domestic exporters to buy the local currency once the selling from interbank players was completed.