Police said about 40 cars and trucks were involved in the pileup that took place 33 kilometers (20 miles) southwest of the capital on the D5 highway.
The D5 is one of the two key routes that link Prague with Germany. It will remain closed for hours.
The regional rescue service said at least six people were injured. Two of them were transported by helicopters to a hospital in Prague.
The Czech Hydro-meteorological Institute warned snowfall is expected across the Czech Republic on Thursday.