Iris Stalzer, 57, is a member of the centre-left Social Democratic party (SPD) and became the mayor of Herdecke in the North-Rhine Westphalia state in September. BBC reported
Local police say a major operation is under way in the small town. Investigators say all avenues are being explored, but they are not ruling out a family connection.
Chancellor Friedrich Merz condemned what he called "a heinous act", adding: "We fear for the life of the mayor-elect, Iris Stalzer, and hope for a full recovery." The SPD said its party members were deeply shocked.
Herdecke's First Deputy Mayor Dennis Osberg wished Stalzer a "speedy recovery", expressing shock and dismay over Tuesday's attack.
Stalzer, who narrowly won last month's mayoral elections and was yet to be sworn in, had multiple injuries to the chest and abdomen, according to German media reports.
Police say she was treated at the scene and then airlifted by helicopter to a hospital in the nearby city of Bochum.
They also said Stalzer's two adopted children - a daughter, 17, and a 15-year-old son - made an emergency call to authorities at midday local time (11:00 BST).
The children were later taken away for questioning and forensic investigation. A reporter at the scene saw a teenager getting into a police patrol car.
