By Billy Stockwell, Sebastian Shukla, Chris Stern and Matthies Otto, CNN

(CNN) — Eighteen people were injured, four critically, in a knife attack Friday in the German city of Hamburg, authorities said.

Hamburg police said they have arrested a 39-year-old German woman, who they believe acted alone in carrying out the attack at the city’s Central Station, after a major police operation. She is in police custody and expected to be brought to a court on Saturday, police said.

Seven people were “badly injured,” while seven others were “lightly injured,” police said. The victims are aged between 19 and 85 years old.

The four critically injured, who include a 24-year-old female, 24-year-old male, 52-year-old female and 85-year-old female, are in a stabilized condition, police said in an upda

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