Wal-Mart shares fell sharply in an instant as volume spiked late on Wednesday afternoon, in an out-of-the-ordinary mini "flash crash," data showed.

In less than one second, the stock of the world's largest retailer tumbled from $78.66 to $78.06. Within a minute, the stock rebounded, with nearly 250,000 shares changing hands between 3:20 p.m. EDT and 3:21 p.m. in 11 exchanges. It was the busiest minute this week in Wal-Mart trading outside of trades at the close.

Seven of the 11 lowest prints were odd-lot trades, or trades of less than 100 shares, and the bid-ask spread widened in some cases to 4 or 5 cents, an unusual occurrence in a widely followed and held stock.

The move mirrors one suffered by nearly two dozen shares in late trading on Tuesday, which forced the cancellation of various trades in shares of AOL .

(Reporting by Rodrigo Campos; Editing by David Gregorio)