Dramatic video footage has emerged of the moment a man wielding a knife was tackled by the Mayor of Jerusalem and his security detail just after the assailant had stabbed an orthodox Jew in an apparently sectarian attack.

The attack happened near one of the entrances to the Old City when a 19-year-old Palestinian Arab who had entered Jerusalem without authorisation stabbed a 30-year-old Hharedi in the abdomen.

The event was witnessed by Jerusalem's mayor Nir Barkat who described what happened.

"I was driving my car near Tzahal Square when suddenly my team saw the terrorist near us with a knife," said Barkat. "Both myself and my bodyguard immediately jumped out of my car, my guard drew his weapon and we held the terrorist until police arrived, and immediately took care of the casualty who fortunately was lightly injured."

In a statement, Israel's voluntary United Hatzalah rescue organization said: "A 30-year-old Haredi male was stabbed in the abdomen by an 18-year-old Palestinian male from the territories, who was in the area of Safra Square without authorisation.

United Hatzalah ambucycle medic Chaim Attias drove up to the plaza arriving at the scene within seconds."

"When I got to the scene I encountered a youth who was stabbed in the stomach," United Hatzalah ambucycle medic Aryeh Yaffe told the Jerusalem Post.

"[The victim] received initial care from members of United Hatzalah's ambucycle unit who arrived first on scene within seconds of the attack. After initial treatment, he was transported to hospital for continued treatment. The victim was conscious and in a stable condition."

Mayor Barkat said the assailant was lucky he dropped his knife when the security detail drew his gun.

"It's clear to me that if the terrorist had continued stabbing, he would not be alive right now. But because he dropped the knife we overpowered the terrorist, and I hope he is punished appropriately."