The aircraft, a sports plane and an ultra-light aircraft, crashed on Sunday just 600 metres outside an airport near Schwaebisch Hall, in the state of Baden-Wuerttemberg.
The dead are almost certainly the pilots, rescue services said.
A search of the sports plane was slowed down by the passenger security systems which could pose dangers for the emergency teams, a spokesman said.
It was also possible that someone had ejected before the crash, meaning that authorities could not give a confirmed figure for the number of people killed.
The search operation was expected to last late into Monday.