Sally Auld, a fixed income and foreign-exchange strategist at JPMorgan, told CNBC's "Street Signs" that markets seem to be biased toward expectations that the U.K. will remain the EU, with the view bolstered by recent polls.
But she doesn't expect much market action heading into the vote.
"I'm not sure market levels are going to change much in the next 36 hours," Auld said. "It seems to be a widely accepted consensus that probably the best thing to do is to reduce risks, stay on the sidelines, wait and see what happens later this week and then proceed from there."
The British pound traded at $1.4685 as of 3:34 p.m. HK/SIN, up from levels near $1.40 in the previous week.
Federal Reserve Chair Janet Yellen, who began her two-day testimony before Congress, said that a U.K. vote to leave the EU could have significant economic repercussions. In prepared remarks, she also said that a cautious approach to monetary policy remained appropriate and while the pace of improvement in the labor market has slowed, it's important not to overreact to one or two labor reports.
The dollar strengthened in the U.S. session against a basket of currencies, despite Yellen's cautionary remarks; the dollar index traded as high as 94.123 during before trimming some of its gains to trade at 93.838 as of 3:36 p.m. HK/SIN on Wednesday. This was compared with levels around 93.576 on Tuesday afternoon Asia time.
Analysts said the move in the dollar could have been driven by markets positioning for the remain camp to win the referendum in the U.K.
The Japanese yen, which is considered a safe-haven currency, strengthened relatively against the dollar in the afternoon session, with the pair trading at 104.42, compared with levels around 104.85 earlier. On Tuesday afternoon local time, the yen traded near a 22-month high at 103.57 against the greenback.
Major exporters in Japan closed mostly lower, with shares of Toyota shedding 0.53 percent, Nissan off 0.79 percent and Honda down 2.41 percent. Sony shares declined 1.83 percent. A stronger yen is a negative for exporters as it reduces their overseas profits when converted into local currency.
SoftBank shares climbed 2.6 percent, beating the broader index. The Japanese internet and telecommunication giant said its president, Nikesh Arora,had resigned. Masayoshi Son will remain CEO longer than originally planned, while Arora will assume an advisory role at the company, which has a shareholder meeting on Wednesday.
SoftBank also said in a statement on Tuesday that it would exit Finnish game developer Supercell, selling its entire stake to Chinese technology firm Tencent in a deal that values Supercell at about $10.2 billion.