Police have a arrested a teenager following the stabbing of a 15-year-old pupil outside a school.
Cardinal Wiseman school in Greenford was closed at the time of the incident, which happened just after 4pm on Thursday, 45 minutes after classes had finished.
It is thought the pupil was involved in a confrontation with youths from elsewhere when the stabbing occurred outside the school entrance.
A 16-year-old from Southall was arrested an hour after the attack.
The injured teenager boy was rushed by air ambulance to an east London hospital where his remains in a critical but stable condition.
A statement from the school said: "Staff were alerted and responded swiftly. Police and emergency teams arrived quickly.
"School will open again as usual on Monday.
"We will be offering a full range of pastoral support for those students affected by this."
An arts festival and a number of school trips have been cancelled following the incident.