A 58-year-old man, thought to be the pilot, and a 54-year-old woman were killed in the crash on Monday near the small town of Parchim, around 150 kilometres north-west of Berlin, authorities said.
A police spokeswoman told AFP that a second man, aged 59, was battling life-threatening injuries and a 61-year-old woman was seriously wounded but not in danger of dying of her injuries.
The cause of the accident was unclear, the spokeswoman told AFP. "We are assuming that the crash was caused by a technical fault," she said.
The four-seater propeller-driven Diamond Aircraft DA42 came down in a meadow a few kilometres after take-off. All four people in the plane were Swiss citizens, police said.