It happened just before 8 p.m. on the 300 block of North 22nd Street at the Parkway.
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Police say a 28-year-old man was stabbed several times in the legs and once in the back of the head. He was taken to Jefferson University Hospital in critical condition.
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No arrests have been made.
Anyone with any information is asked to call police at 215-686-TIPS.
Two encampments have been set up in the city all summer, one along the Parkway and another along Ridge Avenue outside of the Philadelphia Housing Authority headquarters. Camp leaders have said they want safe housing. Negotiating with Mayor Jim Kenney hasn't yielded results, as deadlines for them to leave have come and gone.
Residents in the immediate area have recently expressed fears for their safety.