Police spokesman Jochen Laschke said a regional train heading to the small town of Ibbenbueren from the city of Osnabrueck collided with the trailer of a farmer's tractor that was loaded with a tank full of manure. Laschke said the accident took place in a rural area near Ibbenbueren, 440 kilometres (275 miles) west of Berlin.
Three of those injured were in severe condition, police said.
According to investigators on the scene, the trailer became detached from the tractor's tow-bar and came to a stop on the tracks, Laschke said. The farmer tried to remove the trailer from the tracks but wasn't successful because the barrier gate had closed, he added.
Investigators were still trying to find out how exactly the trailer became disconnected from the tractor.
The train crashed into the trailer and came to a stop 200 metres (650 feet) down the track. The farmer was not injured.
TV video footage showed parts of the trailer lying on one side of the track, the manure tank on the other. The windows and metal parts of the train's engine were torn away by the impact.
"The train was very crowded," Laschke said. "We got an emergency call at 11:31 a.m. today and rescue team, firefighters and psychologists from all over the region were activated to help." Laschke said the passenger who was killed was a woman, but he did not yet have any information about her identity.
The train was operated by a small private train company, Westfalenbahn, and not by national train operator Deutsche Bahn.
Germany is known for the quality of its train service but several other accidents have occurred recently at train crossings in Germany, killing six other people in 2015 alone before Saturday's accident, according to the news agency dpa. Especially in rural areas, train crossings are often not blocked by barrier gates.
In recent months, the country's usually reliable train connections have been hurt by several strikes by German train drivers who are in a dispute with Deutsche Bahn over pay and work conditions.
Germany's worst train accident happened in 1998, when a high-speed ICE train crashed in the northern German town of Eschede, killing 101 people and injuring more than 80.Suggest a correction