The yen touched an 18-month low against the euro on Monday, slipping with emerging Asian currencies as traders tried to assess the economic fallout from tsunami waves that devastated parts of Asia the previous day.
Although Japan was not affected by the giant waves unleashed after a powerful earthquake, traders were nervous about the scale of the disaster, in which over 12,600 people were killed in South and Southeast Asia.
"We have never seen such a catastrophe before so it's hard to predict what will happen with emerging currencies," said a senior trader at a U.S. bank.
"This could trigger a movement in the majors, especially because trading is thin now."
At 2125 EST, the euro bought around 140.55 yen after hitting an 18-month high of 140.70. It fetched 140.27 in late Friday trade.
The dollar moved up to around 104 yen compared with 103.70 in late trade on Friday.
The Thai baht eased to around 39.10 per dollar in early trade, from 38.91 on Friday. The Indonesia rupiah lost half a percent to around 9,310 per dollar.
U.S. stock and bond markets were closed on Friday for a holiday.