Seven people have been taken to hospital after a five-vehicle pile-up which blocked the M26 in Kent.
Two lorries, two cars and a box van were involved in the collision on the London-bound carriageway near Kemsing just after 9.30am.
Among those released from one car were two children, fire chiefs said.
Patients have been taken to four hospitals, including King's College and St George's in London, Secamb said.
The crash closed the motorway in both directions, with police warning drivers that it will stay shut into this evening's rush-hour.
The conditions of those injured have not been disclosed, but they have been ferried to hospitals by South East Coast Ambulance Service (Secamb).
A Kent Police spokesman said: "The M26 is closed in both directions and could remain closed for several hours into Wednesday afternoon and during rush-hour.
"Traffic on the London-bound carriageway is being turned round and redirected back to join the M20 at Wrotham Heath."
A Kent Fire and Rescue Service spokesman said: "Motorists are advised to avoid the area as both carriageways are closed. Kent Police, Secamb paramedics and the Kent Air Ambulance are also in attendance."
The Highways Agency said its contractors were helping emergency services to try to reopen the road.
A spokesman said: "Police investigations are ongoing and it is expected that the closure will be in place for most of today and possibly into the evening peak period.
"Traffic is being diverted via the M25 and M20. Road users are advised to avoid the area, check travel information where possible and to plan alternative routes."
Chief Inspector Pam Flight, of Kent Police, urged witnesses or anyone who left the scene to call the serious collision investigation unit on 01622 798538.