As the chocolate dried under a mild spring sun, long lines of traffic grew on either side of the spill, and the authorities said it would probably be hours before the road was usable again.

“We have to remove the truck from the highway first,” Marlena Kukawka, a media officer for the police in the small town of Slupca, near where the spillage occurred, said in a phone interview. “It will take a few hours or more,” she said about the cleanup.

Ms. Kukawka said firefighters were using streams of hot water to melt the chocolate and wash away the mess.