Paramedics, police and firefighters were called to a crash between at least five vehicles at 1.30pm injuring at least two people.
The incident is causing long tailbacks in the town centre and Rose Kiln Lane and motorists are advised to avoid the area.
South Central Ambulance spokeswoman Ngozi Fakeye said: "There is a road traffic collision involving several vehicles opposite the Citroen garage.
"It is a live incident at the moment, three ambulances are there."
A motorist said: "I could see people being taken away on stretchers.
"There was a van involved, it is smashed to pieces. The other vehicles looked like family cars.
"Traffic is also a bit slow northbound because of rubber-neckers."
Royal Berkshire Fire and Rescue Service (RBFRS) spokeswoman Ellie Gray confirmed crews from Caversham Road fire station were called to the scene but did not have to free anyone from the wreckage.
More to follow.