Three of the casualties were seriously injured, while six suffered less serious injuries and 15 were treated for minor injuries, according to the region’s ministry of health.
All 23 passengers and one driver were injured.
Nationals from Germany, Spain, Poland, Belarus and Lithuania were also injured in the accident, which occurred at 3.10am local time (2.10am BST) on Wednesday near Barcelona’s El Prat airport.
The bus was transporting tourists from the resort of Lloret de Mar.
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A Foreign and Commonwealth Office spokeswoman said: “We are in contact with Spanish authorities following a coach crash in Barcelona and are ready to help any Britons involved.”
Ambulance, police and the fire brigade crews attended the scene on the B-10 highway.