Emergency services are currently dealing with huge crashes on both motorways which are thought to have caused serious injuries
Motorists are facing huge delays following two serious crashes on the M40 and M1 motorways.
Three people have been confirmed dead following a crash on the M1 between junctions 12 and 13.
At least one person has also died following a 30-car pile-up on the M40 between junctions 9 and 10 northbound.
Read below for live updates.
Fog played major role in M40 pile-up, say police
Fog played a major part in the M40 pile-up, according to police.
Chief Inspector Henry Parsons of Thames Valley Police Roads Policing said: “The cause of this collision is under investigation, however, we believe that fog played a major part.
“This has been an extraordinarily large collision, we have not had a collision on this scale for many years in Thames Valley and one man has sadly lost his life.
“We are working as quickly as possible to clear the area and get the traffic moving again.
"I would like to thank the public for their patience while we undertake our important investigative work before a full reopening of the road is possible.
“Should anyone have concerns about friends or relatives who may have been travelling on the M40 this morning, then they can call our non-emergency number 101 for assistance.”
Video: Slow-moving traffic on M1 following fatal crash
This video shows slow-moving traffic on the M1 after today's fatal crash.
Pictured: Aerial image of the M40 pile up
This photo shows the aftermath of the M40 pile up from the air.
Some 30 vehicles were involved in the smash between junctions 9 and 10 northbound this afternoon.
One man died and another person is "critically ill" in hospital.
Six motorists were seriously injured and more than 50 suffered minor injuries.