A truck sped into a US military convoy on Autobahn 3 in Bavaria.
The vehicles caught fire, a police spokesman said.
Eight members of the US Army were believed to have come to the hospital for a check-up with smoke poisoning.
The police assume an accident and not an attack.
On Monday, shortly after the junction in Parsberg in the Neumarkt district in the Upper Palatinate, the semitrailer truck drove into the convoy that had been standing on the hard shoulder with several vehicles, including a tanker.
Several vehicles went up in flames.
The truck was loaded with sawdust and initially there was no precise information about the condition of the driver.
He rammed the military vehicles with full force.
A spokesman for the US Army in Grafenwoehr said that no information about injured US soldiers was yet available.
The vehicles in question were US Army vehicles, and exactly which vehicles have yet to be determined.
Why they stopped on the hard shoulder is still unclear.
The highway was closed in both directions, the police spokesman said.
The fire was out.
The public was never in danger because the smoke was not moving towards populated areas.