A 15-year-old boy in police custody has managed to trick police and escape the Southport Watchhouse.

The boy faced the Southport Children's Court on Saturday morning over charges relating to an alleged carjacking that happened on Thursday and had been ordered to remain in custody. 

The South Eastern Regional Duty Officer, Senior Sergeant Brett McGibbon said the boy escaped bout 10.40am Saturday after he posed as another juvenile, was bailed and ran from the watchhouse. 

"It is a bit embarrassing," Senior Sergeant McGibbon said.

"Obviously this matter is subject to an internal review to exactly determine what has occurred but patrols at this stage failed to locate the male.

"We're very interested in having them returned to custody."

Senior Sergeant McGibbon said the escapee had been sharing a cell with another juvenile, who he then posed as.

"It certainly appears it was a deliberate attempt to abort remaining in custody," he said.

"It was realised by the watchhouse staff immediately that they've released him. They'd just checked photos and in the space of approximately 30 seconds or getting from one door to the other he's been able to jump over a gate."

It is understood the boys were of similar age, but visually different.

Senior Sergeant McGibbon said police were continuing to search for the boy but urged the juvenile to hand himself in to police. 

The boy is described as Caucasian in appearance, of a slim build, about 176 centimetres tall with light brown hair and blue eyes.

He was wearing long black trousers and a dark blue shirt.

Anyone who may have seen the boy should contact police on 131 444.

EARLIER:

A teenage boy has been charged after what police described as an attempted carjacking on the Gold Coast that left a girl fighting for her life in hospital.

The pair allegedly pulled a knife on a 24-year-old woman and demanded her car after she offered them a lift from Harbour Town shopping centre on Thursday night.

Police say the panicked driver drove away and hit the 15-year-old girl, causing serious injuries.

Unaware the girl had been injured, the woman called police after driving a short distance to report the attempted robbery.

The 15-year-old boy allegedly fled the scene and was arrested on Friday.

He has been charged with unlawfully entering a vehicle while threatening violence and is due to appear in a Southport Childrens Court on Saturday.

The girl was placed in an induced coma and remains in critical condition at the Gold Coast University Hospital.

- with AAP