British Transport Police said they were violently assaulted following a dispute over the queue at the taxi rank outside Hull Paragon Interchange.
The incident happened shortly before 4am on August 19, when the victims were stood at the front of the taxi queue and another man went in front of them and tried to get into a taxi.
An argument broke out between the pair and the man and the group of people he was with. The man pulled their woman's hair before punching her, causing her to fall back and knocking her unconscious.
The male victim tried to defend her and was pulled to the floor by a woman who was with the group, and he was then punched while on the ground by another man and knocked unconscious.
BTP said the man suffered serious head injuries including a large wound to the back of his head, and cuts to his cheek. The female victim suffered scratches to her face.
The three people in the group are described as a man with short brown hair, wearing all black with a grey hood, another man wearing dark blue jeans and a grey t-shirt, and a woman with brown hair, wearing blue jeans, a brown shirt, and a black jacket with a bag on her right side.
BTP said they are keen to speak to anyone who may have witnessed the attack to help with their investigation. Anyone with information is asked to contact BTP by texting 61016 or call 0800 40 50 40 and quote reference number 51 of August 19, 2021.