The River Sava has burst its banks, affecting Croatia to the north and Bosnia-Hercegovina to the south, and Serbia to the north and south further downstream. The peak of the flood surge is not expected in parts of Serbia until Wednesday.
Any further flood surges could threaten Serbia's Nikola Tesla power plant in Obrenovac.
The agricultural sector, an important part of Serbia's and Bosnia's economies, is likely to be hit severely.
Damage to the Kolubara power plant is estimated at more than $100m on its own.
Serbia and Bosnia are at the upper end of emerging market penetration levels in terms of insurance, while Croatia is closer to a full developed market. Major layers in the region include Dunav osiguranje in Serbia, Croatia osiguranje in Croatia, Sarajevo osiguranje in Bosnia, Austria-based Uniqa in Bosnia and Serbia, Allianz in Croatia, Generali PPF and Vienna Insurance Group.
Even though insurance penetration is not at full developed market levels, the damage which appears to have been incurred in the commercial sector makes it likely that there will be an impact on insurers with interests in the region.