The woman, who is around 60 years old and reportedly an active member of the city's Jewish congregation, was on Tuesday afternoon in hospital being treated for life-threatening injuries.
Police stationed officers outside von Platenska Huset, the historic villa which serves as the city's synagogue, after the stabbing.
"We don't know if it's a coincidence or if the attack has something to do with her being active in the congregation," one of the congregation's members told Swedish state television broadcaster SVT.
"We are deeply shocked. It's a really wonderful and helpful person who has been subjected to this tragic event."
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Filip Annas from the local Helsingborg police said that they received the first reports of the stabbing at 7.30am. He could not immediately confirm whether the woman knew the attacker, who fled the scene before police arrived, or not.
Regional newspaper Helsingborgs Dagblad reported that witnesses heard a woman scream "help me, help me" in English.
Police are currently looking to interview any witnesses.
A police source told the Sydsvenskan newspaper that officers were as yet unsure if the attack was anti-Semitic. "That is something we are analyzing right now," the source said.
After police managed to identify the suspect late on Tuesday, they said they no longer suspected any anti-Semitic motives.
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