A man was stabbed near a McDonald's restaurant after earlier confronting another diner for allegedly eating some of his meal.
The 26-year-old is in a serious but stable condition in hospital after the attack, which happened at the junction of Chadwick Road and High Road in Ilford on Monday night.
Police say the victim went into the nearby McDonald's with a woman and ordered some food, but returned to the counter minutes later to complain that some of it had been eaten.
He then accused another customer of being responsible and a row broke out.
Police say the victim then left the fast food outlet but was followed by two suspects and two other youths.
A fight then broke out in the street and the man was stabbed once in the chest.
The two suspects then ran off down Cranbrook Road, past Ilford station and into York Road, police say.
It happened at around 10.20pm.
Woodford Bridge councillor Paul Canal witnessed the aftermath after coming out of Redbridge Town Hall following a council meeting.
Cllr Canal said that he and fellow councillors David Poole and Matthew Chaudhury went to see if they could help but police and ambulance crews arrived quickly at the scene.
He told the Guardian : "The police and paramedics were very worried. They described it as 'touch and go'."
"It is shocking that such an attack can happen at 10pm on a Monday evening in Ilford.
"The side street, whilst close to Ilford, is not very well lit.
"I hope the victim recovers fully and the perpetrators are quickly apprehended and punished".
A Met spokeswoman said: "Both suspects are described as black males aged between 18 - 25 years old, having short black hair and wearing dark coloured puffer type jackets and dark coloured tracksuit bottoms.
"One of the suspects may have a silver tooth.
"Anyone with information about this assault is asked to contact DC Rush at Ilford CID on 0208 345 2733 or to remain anonymous, call Crimestoppers on 0800 555 111."