An Audi A4 hit the area outside Streets nightclub, John Street, Porthcawl, Bridgend county, on Sunday at 01:00.
The man was arrested on Sunday on suspicion of drink-driving and dangerous driving.
The injured, aged between 17 and 43, were taken to hospitals in Bridgend and Swansea - most with leg injuries.
An 18-year-old woman is helping South Wales Police with their inquiries.
Eyewitnesses described their "total shock" and reported seeing a white car being pursued by a police van shortly before the incident.
Police could not confirm or deny whether a police car was involved but said "an internal investigation is under way".
The Independent Police Complaints Commission (IPCC) has also been informed.
It is understood that seven men and six women in total were injured.
On Sunday, the Abertawe Bro Morgannwg health board said three of those injured and taken to the Princess of Wales Hospital in Bridgend had been treated and discharged.
The remaining six people have sustained serious injuries but were in a stable condition.
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.
A health board spokesperson said additional hospital staff had to be called in to deal with the casualties after a "major incident" was declared.
Police are continuing to question a 24-year-old man after 13 people were hurt when a car crashed into a smoking area outside a nightclub.