A renewed advance in the dollar is sending Asian currencies to multi-month lows while prompting authorities in China and Japan to step up defense of their beleaguered exchange rates.

Japan issued its strongest warning against rapid declines in the yen in weeks on Wednesday, with its top currency official saying the nation is ready to take actions amid speculative moves in the foreign-exchange market. Shortly after, China’s central bank offered the most forceful guidance with its daily reference rate for the yuan, as the currency weakened toward a level unseen since 2007.

The moves came as the Bloomberg Asia Dollar Index — a gauge of currencies in the region — fell toward lowest close since November amid greenback gains. A gauge measuring strength in the US currency traded around a six-month high as a resilient economy underscored the case for elevated interest rates.

The yen and yuan are among worst performers among Asian currencies this year as their wide monetary policy divergence with the US drive outflows.

While Japan stopped short of using more aggressive tools to support its currency, China has already sought to bolster the yuan by asking state-owned banks to sell dollars while tightening liquidity offshore to squeeze short currency bets.

--With assistance from Ruth Carson.