Zimbabwean authorities have seized more than $50m worth of old banknotes at roadblocks and border posts in a crackdown on money launderers.
Inflation in Zimbabwe is the highest in the world
People are rushing to make a deadline in 12 days' time to deposit their cash after the introduction of new currency.
Anyone carrying more than $400 in old currency is liable to have it seized.
The central bank head said last week over $80m worth was not in circulation, hinting it might be stashed outside the country for speculative purposes.
The central bank unexpectedly devalued the currency last week, lopping off three zeros off banknotes, in an attempt to stem both corruption and hyperinflation of more than 1,000%.
Banknotes worth about $40m were discovered in containers at Harare international Airport, Zimbabwe's Herald newspaper reports.
More than 3,000 cases of suspected money laundering by individuals and companies trying to spend their old banknotes rather than officially declare them are also being investigated, the newspaper says.
Local journalist Brian Hungwe says there have been complaints of harassment as the police crackdown, code named Operation Sunrise, gathers pace.
He told the BBC that the use of young people from national military training camps is making many angry.
People have complained that their foreign currency, and local currency in quantities below the stipulated $400 limit, are being seized by the youths at roadblocks and border posts.
Women have complained of being stripped bare by the youths.
In rural areas there is confusion about the new values of the notes and complaints that there has not been sufficient time to warn people to deposit the old currency before 21 August.
Although new banknotes have been issued, they are not widely in circulation and many Harare residents complain that there is a shortage of cash.
In the long term, correspondents say the devaluation is likely to be relief to ordinary people who have to carry huge stashes of cash in boxes or satchels to do weekly shopping.
Businesses, meanwhile, will not have the headache of dealing in figures of trillions which has proved a nightmare for their computer systems.
But with unemployment at more than 70%, many companies continue to close down.
President Robert Mugabe's government blames the economic problems on international sanctions.