An Audi A4 hit the area outside Streets nightclub, in Porthcawl, Bridgend county in South East Wales, early morning.
The injured were aged between 17 and 43, with nine taken to hospital in Bridgend and four to Swansea - most with leg injuries.
A 24-year-old man has been arrested on suspicion of drink driving and dangerous driving, the BBC reported.
An 18-year-old woman is helping South Wales Police with their inquiries. Both have been taken to Bridgend police station.
More From This Section
Rachel Jones, 17, said her friends were injured in the incident and were undergoing surgery.
"A lot of my friends were out actually, so it's really worrying that I could have been out and it could have been me, or one of my friends could have been killed," she said.
Josh Manly, also 17, said he was "totally shocked" to hear his friends had been hurt.
"One has broken his leg, another woke up and couldn't feel his legs," he explained. "We are just shocked."
The Abertawe Bro Morgannwg University Health Board said three of those injured and taken to the Princess of Wales Hospital in Bridgend have been treated and discharged.
Those taken to Morriston Hospital in Swansea include two 18-year-old men, a 21-year-old woman, and another woman who is 38.
Two are in a serious but stable condition, while the other two were admitted as a precaution.
Superintend Andy Valentine said: "This was declared a major incident by the police and ambulance services. All three emergency services were deployed to the incident and worked seamlessly to provide a fast and efficient response."
Nick Smith, of the Welsh Ambulance Service, confirmed: "The injuries were all to lower limbs with no-one reported in a life-threatening condition."