Black market exchange rates — fueled by the central bank buying at the illegal rates to pay the mounting debts of crumbling state fuel and power utilities — rose to upward of 300,000 Zimbabwe dollars to one U.S. dollar in large offshore deals, said one trader.

The official exchange rate is 15,000-1.

"It’s gone crazy," said the trader, who spoke on condition of anonymity because his dealings are illegal. "People are holding out for the highest bidder and mentioning as much as 400,000-1 which could be tomorrow’s price. It’s changing by the hour."

The going rate doubled since Monday, he said

In local deals, the U.S. currency fetched at least 140,000-1 in cash and around 200,000-1 in electronic bank transfers. Shortages of Zimbabwe bank notes created the premium on bank transfers, said the illegal dealer.

Zimbabwe has the world’s highest rate of inflation, estimated officially at around 4,500 percent but calculated by independent finance houses at closer to 9,000 percent.