Two days of negotiations began in Washington on Thursday, and traders are waiting to see whether Chinese and US officials can salvage a deal to prevent more US tariff increases.
"The dominating headlines this week really have been about trade," said Minh Trang, senior foreign exchange trader at Silicon Valley Bank, and "traders are moving towards safe-haven currencies and they're parking it there."
Currency moves this week in response to the latest trade developments have been fairly muted, but Thursday's jump in the yen and the Swiss franc - which tend to attract demand in times of strife - suggested investor nerves have begun to fray.
The yen was 0.35% stronger midafternoon, having pared back some of its gains to trade at 109.7 to the dollar.
The dollar bought 1.015 Swiss francs, though earlier in the day traded at 1.013, the weakest since April 18. Some investors predicted both safe havens have further to run.
"The foreign exchange market still needs to play catch-up.
We certainly haven't seen the volatile moves we would have expected under a scenario like this," said Dean Popplewell, chief currency strategist at Oanda.
"The go-to currency risk-aversion plays like Swiss or yen - the actual rally in those currencies still has some ways to go to fully price in a trade war."
The main casualties have been the Australian dollar, a proxy for Chinese economic prospects, the US dollar and the offshore Chinese yuan.
The dollar index was 0.21pc lower, last at 97.415.
The yuan fell to a four-month low of 6.863, but was last down 0.43pc to 6.837.
"The Chinese yuan really is the world's most important currency," said Societe Generale analyst Kit Juckes. "It isn't the most traded but is an anchor of stability for all markets and if that anchor is dislodged, it will lead the dollar and yen higher."
US President Donald Trump said on Thursday he was taking steps to authorize new tariffs on $325 billion in Chinese imports as officials prepared for last-ditch talks to avert an escalation of a trade war that threatens to derail the global economy.