Faced with world-high inflation that has made its money increasingly worthless, the government is trying to introduce new bills in denominations up to 200 times higher than the old ones.
But the plan went off the rails when President Nicolas Maduro ordered the 100-bolivar note removed from circulation before the new bills arrived.
Formerly the highest denomination bill, the 100-bolivar note was worth about three US cents, and accounted for 77 per cent of the cash in circulation in Venezuela.
In the second city of Maracaibo in the west, groups of protesters hurled stones at police, reports said.
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In the eastern city of Maturin, dozens of people blocked off a major avenue and looting broke out.
"I went by the market and it was being guarded by the military. A chicken truck was looted," Juan Carlos Leal, a farmer in Maturin, told AFP.
In the eastern city of Puerto la Cruz, "people rioted because they wanted to take out money and they weren't allowed to," said Genesis, a local baker.
Protests were reported by users on Twitter in several other states.
Local media in the western city of Santa Barbara said four people were injured when the drivers of a security truck transporting money opened fire on people trying to break into it.
In the capital Caracas, thousands of Venezuelans from around the country queued to rid themselves of 100-bolivar notes at the only place still accepting them: the central bank.
"The world has turned upside down. Normally, there's no food. Now there are no bills to buy it," said Jesus Garcia, a 21-year-old food vendor who had been in line since 4:00 am.
Maduro has presided over an unraveling of Venezuela's oil-rich economy as crude prices have plunged.
The import-dependent country is desperately short of food, medicine and basic household goods.
Venezuela currently has the world's highest inflation rate, set to hit 475 per cent this year, according to an IMF forecast.