Czech police found around 30 migrants, one of whom was dead, in the back of a truck on Monday night.
The truck was stopped along a stretch of motorway between Prague and the eastern German city of Dresden.
"All these persons have been detained," police said on social media.
"We have no information suggesting someone has managed to escape."
The Czech Republic is a popular transit route for migrants seeking to reach Germany and other wealthy European countries.
Migrants found 'in poor health'
Police said they were first alerted to the group of irregular migrants from a report that one of them had died.
Private emergency service ASCR was present at the scene and said that it treated a woman aged around 30 years old who was unconscious.
"A doctor declared her dead after resuscitation lasting dozens of minutes," the emergency service said.
The ASCR said the other migrants were "in poor health" but did not need to be hospitalized.
