The blue-chip BET index of the Bucharest Stock Exchange (BVB) lost 9.04% to 3,609.62 points by 0801 GMT, and the BET-FI index, which tracks Romania's five regional investment funds, the SIFs, sank 14.64% to 19,284.43 points.
Sofia bourse's blue-chip SOFIX index sank 7.32% to 606.49 points and the broader BG 40 index plunged 6.09% to 155.19 by 0802 GMT.
The markets in Asia and Europe opened strongly in the red on Wednesday on concerns the credit crisis will deepen and will lead to global recession.
Stock markets in southeastern Europe have been losing ground in the past month, dragged down by panic selling on international markets following bank collapses in the U.S. and Europe.