Within ten minutes of opening, the benchmark OMXS-index had fallen to 237.0, or 4.4 percent.
Bank stocks were among those with the toughest start to the day, with Nordea shares down 5.9 percent and SEB off 9.0 percent.
Shares in Swedbank were off 8 percent, while stock in Handelsbanken had dropped 5.6 percent in early trading.