"The US dollar is being sold," said Derek Rankin, director at Rankin Treasury Advisory.
"The market has been expecting the Federal Reserve to raise interest rates at some stage this year. The odds of them raising in September is now diminishing rapidly and expectations are moving to December. All year people have actually expected interest rates to go up and the problem they have got is they have got no inflation to justify it."
Investors now see a 34 per cent chance the Fed will hike at its September meeting, down from almost 50 per cent at the start of last week, futures show, while the probability of an increase at or before the Fed's December session fell to about 60 percent from 74 per cent, according to Bloomberg on Friday.
"The data has just been overwhelmingly not supportive of them raising interest rates," said Rankin. "Demand is falling and it is very low around the world. A sell off in world sharemarkets raises concerns about world conditions."
The kiwi also rose because a number of investors were betting on its decline and had to buy back the currency as it gained to limit their losses, Rankin said.
"If it gets above 67.50 (US cents) with any kind of speed this week, then it will be out of the downtrend," he said.
In New Zealand today, Reserve Bank deputy governor Grant Spencer is giving a speech about the property market.
The New Zealand dollar advanced to 91.25 Australian cents from 90.49 cents on Friday, gained to 42.42 British pence from 42.20 pence, slipped to 80.97 yen from 81.42 yen, was little changed at 58.82 euro cents from 58.68 cents, and rose to 4.2504 yuan from 4.2384 yuan.