The incident happened near Willesden Green station in Station Parade at 9pm yesterday (June 25).
Officers and London Ambulance Service crews attended and found four people injured.
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.
There are no concerns about any impact to the wider community.
The incident happened outside a nearby mosque, however it is not believed to be any link to the venue.
Anyone with information about what happened is asked to call 101 quoting CAD 8601/22Jun.
To remain anonymous contact the independent charity Crimestoppers on 0800 555 111 or visit crimestoppers-uk.org.
This is a breaking news story. More to follow.
