More than 70 homes lost power after the crash affected a power cable in Rhondda Cynon Taff.
Firefighters worked to free people trapped at Trebanog Road in Porth at about 09:00 BST on Wednesday.
Three of those injured were taken to hospital – two to University Hospital of Wales, Cardiff, and one to Royal Glamorgan Hospital in Pontyclun.
Three people were freed from the wreckage while a further two managed to get out themselves.
The road is expected to stay shut “for some time” and South Wales Police asked people to avoid the area.