Two men suffered life-threatening injuries after being stabbed outside two London stations.
Officers were called to Forest Lane, near Forest Gate and Wanstead Park stations, shortly before midnight on Thursday, the Metropolitan Police said.
The two victims, aged 19 and 23, are in a critical but stable condition, a spokesperson said.
A 17-year-old has been arrested on suspicion of attempted murder and taken into custody.
Scotland Yard said a Section 60 order, allowing officers to search anyone they suspect of carrying an offensive weapon, was in effect.
It came hours after an 18-year-old man was stabbed in the leg in Walthamstow.
He was taken to hospital in a critical condition, but his injuries were later confirmed to be non life-threatening.
