The closure was between the Marcham and Hinksey Hill Interchanges.
The Northbound carriageway was shut for several hours this morning (04/12) after a caravan overturned.
Emergency services were called to the scene shortly after 6am.
Around 3 other vehicles are reportedly involved.
Ambulance crews say one person has been taken to the John Radcliffe Hospital in Oxford, their injuries are not thought to be life-threatening.
There are also unconfirmed reports of gas bottles on the road.
The Oxford Bus Company said the A34 closure is causing major delays on its Abingdon services.
The A34 is currently closed between the Marcham interchange and Hinksey due to a collision involving multiple vehicles.— TVP Roads Policing (@tvprp) December 4, 2017
Drivers are advised to avoid the scene if possible.
We will provide updates when we are able to do so.
Highways England said the Northbound carriageway would remain closed for several hours for collision investigation work by Thames Valley Police.