Prime Minister Benjamin Netanyahu condemned the attack, the worst at the event in years, as “a most serious incident”.
Around 5,000 were waving banners as they marched down an avenue in the Israeli capital, when the attacker jumped into the crowd and “started stabbing everyone in his way”, one witness said.
Pictures from the scene (above) showed bystanders apparently overpowering a man and disarming him.
Two of the injured are in a serious condition, medics said.
Police said they had arrested the suspected perpetrator and were questioning him.