People in Zimbabwe rushed to shops and banks on Monday to spend or exchange old banknotes before they ceased to be legal tender at midnight (2200 GMT).
Long queues formed at banks as people tried to convert their savings
Three weeks ago Zimbabwe adjusted its currency, removing three zeros from the values after years of high inflation.
The central bank indicated that it might allow extensions to the deadline in exceptional circumstances.
But the authorities insisted that the roll-out of the new currency, meant to tackle hyper-inflation, would go ahead.
Supermarket owners in the capital, Harare, reported that business was unusually brisk for a Monday, as people tried to spend their old cash.
There were also reports that buses and some shops were already refusing to accept the old notes, and that long queues were forming at banks as people tried to change their old money.
Some banks stayed open more than two hours late to deal with the crowds, AFP news agency reported.
Zimbabwe has endured inflation rates of nearly 1,000%.
The new currency is intended to end the necessity of carrying bags of cash for even small purchases, and eliminate the multiple zeros that Zimbabweans have become used to seeing on price tags.
A loaf of bread, for example, will now cost 220 Zimbabwe dollars, as opposed to 220,000 old Zimbabwe dollars.
Fears have been expressed about residents of remote rural areas who may not have heard about the currency change, though the head of the central bank has reportedly said those with "genuine cases" would be treated fairly.
Critics also charge that the measure does not tackle the underlying causes of Zimbabwe's inflation.
They accuse President Robert Mugabe of ignoring economic principles and trying to bribe voters by seizing productive white-owned farms to give to poor black families.
He maintains that Zimbabwe's economic woes are the result of a Western plot intended to bring down his government.
Nearly two weeks ago, the authorities seized more than $50m worth of old banknotes at roadblocks and border posts in a crackdown on money launderers.