Brisbane police have arrested a man they say is helping with their inquiries into how another man fell 30 metres from a CBD balcony.

A man has been arrested by police investigating how another man fell from the fifth floor balcony of a Brisbane building.

A 28-year-old man suffered head injuries after plummeting about 30 metres from a highrise balcony on Upper Roma St, in the CBD, on Sunday morning.

Officers investigating how he fell announced they had arrested a 36-year-old man on Wednesday afternoon.

The injured man is in a critical condition in the Royal Brisbane and Women’s Hospital.