Police were called to Imperial Drive, Harrow at 11:03hrs on Sunday, 5 July to a report of a stabbing outside a property.
Officers and London Ambulance Service attended and two men were at the scene suffering stab injuries.
They have been taken to hospital where one man is in a critical condition and the other is in a non-life-threatening/changing condition.
No one else is believed to be involved in the incident.
No arrests; enquiries continue.