At least one person is understood to have died in a 40-car motorway pile-up in fog this morning.
Fire crews, police and ambulances rushed to the scene, where paramedics are assessing more than 30 patients for possible injuries.
Long queues of traffic have built up following the crash, which happened between junctions 9 and 10 on the M40, near the designer outlet shopping centre in Bicester, Oxfordshire, just before 7.50am.
The AA said the area was busy with traffic as families hit the roads for the start of half-term break.
Pictures posted on Twitter show cars at a standstill in thick fog on the motorway, while drivers and passengers stand around.
Forecasters said Oxfordshire was hit by fog this morning, which would have hampered visibility.
An ambulance spokeswoman said it is too early to know the nature and severity of the injuries suffered by drivers.
“We have a lot of resources on the scene - ambulances, our helicopter ambulance, rapid response vehicles, our doctor and our hazardous area response team.”
Thames Valley Roads Policing said: “M40 Northbound J9 will be closed for a number of hours following a fatal collision. Officers are working to relieve the traffic stuck northbound.”
Meanwhile, a section of the M1 was closed following a collision between a double-decker coach and a stationary car in Bedfordshire.
Bedfordshire police said the three men travelling in the car, which had stopped on the hard shoulder, were pronounced dead at the scene near Flitwick.
No one on the coach, which was heading north from the Kent area, was hurt in the crash at about 6.45am, but a fourth occupant of the car was taken to hospital in Oxford with serious injuries.
PA