The incident happened in Willesden Green station in Station Parade at 9pm yesterday (June 25).
Officers and ambulance crews found two men – 20 and 21 – with stab wounds.
They were taken to hospital in a critical condition.
A 20-year-old woman reported breathing difficulties but refused medical attention.
A third man, aged 20, was arrested on suspicion of attempted murder and remains in custody.
He also received treatment for stab wounds deemed not to be life-threatening.
There were initial concerns about a suspected chemical have been involved, but the incident is no longer being treated by police as chemcial related.
A Met spokesperson said: “Police were called at 21:00hrs on Wednesday, 25 June following reports of a stabbing in Station Parade, NW2.
“Officers and paramedics attended the scene.
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“Two men, aged 20 and 21, were taken to hospital with stab injuries. They remain in hospital in a critical condition.
“A 20-year-old woman, who reported breathing difficulties, declined medical treatment at the scene.
“A separate 20-year-old man was arrested on suspicion of attempted murder. He currently remains in police custody.
“He also received medical treatment for stab injuries that were deemed not to be life-threatening.
“Specialist resources were deployed following concerns about a suspected chemical.
“These have since been stood down and it is not being treated as a chemical incident.”
