The value of the Zimbabwean dollar suffered its worst crash in memory, dealers said Thursday, sparking a run on dollars and forcing stores to close early to put new prices on their meager stock.

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