The incident happened in Cranbrook Road, near Ilford Elizabeth line station, just after 8pm yesterday (September 16).
Officers and medics from the London Ambulance Service arrived and found the teenager with stab wounds.
He was rushed to hospital where his condition is not believed to be life-threatening or life-changing.
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There have been no arrests but an investigation is ongoing, with officers appealing to the public for information.
A spokesperson for Metropolitan Police said: “Police were called at 20:05hrs on Tuesday, 17 September to Cranbrook Road, Ilford following reports of an altercation.
“Officers attended and found an 18-year-old man with stab wounds. He was taken to hospital and his condition is not believed to be life-threatening or life-changing.
“No arrests have been made at this stage and enquiries are ongoing.
“Anyone with information is asked to call police on 101 or online quoting CAD 6852/16SEP. Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.”
A London Ambulance Service spokesperson said: “We were called at 8.06pm yesterday (16 September) to reports of a stabbing in Cranbrook Road, Ilford.
“We sent an ambulance crew, a paramedic in a fast response car and an incident response officer to the scene.
“The first paramedic arrived in around six minutes.
“We treated a patient at the scene and took him to a major trauma centre as a priority.”
