Jacx, who did not give his full name, works at JJ Fruit and Vegetables outside Seven Sisters station and said his friends witnessed the stabbing.
He told the Telegraph: “They said he was an old white man with a beard who was begging and hanging around here.
“My friends had pale faces. They were so white, they were so scared.”
A British Transport Police spokesperson said: “Officers were called to Seven Sisters tube station at 8.48am today (23 July) to reports of a serious assault.
“Paramedics also attended and a man was taken to hospital with injuries consistent with a knife attack. His injuries are believed to be life-threatening.
“Two women were arrested on suspicion of assault and battery. Another was also arrested on suspicion of common assault. They remain in police custody and the investigation is ongoing.
“The metro station remains closed while officers investigate, and passengers will see a heightened police presence in the area.
“Anyone with information can contact British Transport Police by texting 61016 or calling 0800 40 50 40 with reference 171 of 23 July. Alternatively, you can contact Crimestoppers anonymously by calling 0800 555 111.”
