An elderly man who was allegedly bashed by a teenager inside his northside Brisbane unit has only a 25 per cent chance of surviving, a court has heard.

Tyler Jay Austin, 18, who is charged with causing grievous bodily harm and entering a dwelling with intent, has been granted bail in Brisbane Magistrates Court.

Austin is alleged to have assaulted Richard Bland, 71, inside Mr Bland's unit in Allworth St, Northgate, on Tuesday night.

It will be alleged that Austin forced his way into Mr Bland's unit around 7pm on Tuesday night.

He allegedly assaulted the elderly man by striking him multiple times on his head and body.

Austin then fled to a nearby unit, but was arrested by police a short time later, it is alleged.

Police prosecutor Senior Constable Hayley Kipps told the court the alleged victim's injuries were so serious that he had only a 25 per cent chancing of surviving.

Neighbour Jeff Bonnici, who lives under the 71-year-old man's unit, claims he heard screaming in the lead-up to the incident.

The Courier Mail understands the 18-year-old man didn't live in the building.

Another neighbour said she saw the 71-year-old man being stretchered out by ambulance around 8pm with a neck brace on.

She said emergency services are often attending to situations at the units on Allworth Street in Northgate.

Police declared a crime scene at the unit and the door has been boarded up with a plank of wood with a pair of medical gloves at the entrance.

Detectives were at the scene again today speaking to neighbours.

Austin lives with his parents at Caboolture and he was granted bail on conditions that he continue to live there and report to police three times a week.

He is not allowed any contact with Mr Bland and is not to go within 200 metres of the unit complex where Mr Bland lives.

Originally published as Teen bailed over alleged bashing of old man in unit