Demonstrations reached boiling point at the main bazaar in Tehran – the centre of trade and foreign exchange dealing.
Images from an unverified amateur video show protesters angry at the collapse of the rial, the Iranian currency.
Its value has plunged to record lows against the dollar.
Reports indicate tear gas was used and that there were arrests.
The central bazaar – whose merchants played a major role in Iran’s revolution of 1979 – was closed on Wednesday.
Western economic sanctions imposed over Iran’s disputed nuclear programme have hit the country’s earnings from oil hard.
With Iran’s official inflation rate at around 25 percent the currency weakness is hurting living standards.
There has been a run on trading in hard currencies pushing down the rial. The government has blamed speculators for the currency collapse and have reportedly ordered security forces to take action against them.