A man is in a critical condition in hospital after a violent night on the streets of Adelaide that saw seven people arrested.

South Australia Police say a fight broke out between two groups at the corner of Hindley and Morphett streets.

A 19-year-old Morphett Vale man suffered critical head injuries after falling onto concrete at 2:00am.

A 21-year-old man, also from Morphett Vale, has been charged with aggravated assault causing serious harm.

He was refused bail and will appear in the Adelaide Magistrates Court tomorrow.

At the same location in June, a man was knocked unconscious in a fight.

And in December, a man died after a brawl at the same intersection.

Also last night, ambulances took two men to hospital after a fight at the corner of North Terrace and Pulteney Street about 10:00pm.

Both of them had non-life-threatening injuries and are in a stable condition.

Five men and a woman in their 20s have been charged with aggravated affray over the incident and will appear in court in November.