The mother of a 14 year-old Noongar boy held in an adult prison said she has not been able to speak to her son after a fire in his unit on Sunday night.

Crystal Mason said she first read about a fire at unit 18 in Casuarina Prison, a maximum security adult prison, on social media in the early hours of Monday morning.

Unit 18 is a standalone unit for children moved from Banksia Hill Detention Centre in Western Australia.

Ms Mason said Casuarina and Banksia Hill prison staff repeatedly hung up on her while she was trying to understand what had happened.

"From 2am this morning I didn't know what to do as a mum, my son was in there," she said.

"I was trying to find out if it was true.

"At 6am I called my mother, and I called Megan Krakouer (a member of the state's prisons suicide task force and the National Suicide Prevention and Trauma Recovery Project) as well."

Ms Mason said she received a call at about 10.45am from a prison officer at Casuarina who said they were informing parents and guardians there was an incident and a fire.

The fire is understood to have started about midnight, at which time children were removed from the unit which allegedly led to a fracas.

"The kids turned on them and attacked them, the officer who rang me this morning said," Ms Mason said.

"They couldn't answer how my son is, they told me the boys have been checked by the medic.

"I need to hear from him myself so I can be sure he is OK.

"It is very distressing to read there is a fire inside the jail. I am very stressed."

Ms Mason said she had no received any indication of how her son is or when she may be able to speak with him.

Her son is due in court tomorrow.

A Department of Justice spokesperson said the department was investigating "an overnight incident" at the facility.

"Staff extinguished a cell fire and tended to a few small spot fires which had been lit in the corridor," they said.

"As part of standard practice, DFES attended the facility but were not required to deploy as the fires had already been put out.

"The young people were evacuated to a safe area of Unit 18 as a precaution during the incident and later returned to their cells."

The department confirmed one of the children was treated for smoke inhalation and has since returned to the unit.

"These detainees are being accommodated in Unit 18, a more secure temporary facility, while vital infrastructure upgrades are carried out at Banksia Hill Detention Centre," they said.

In July advocates for the youth detainees said moving a group of them to Casuarina was a "recipe for disaster".

In August it was revealed there had been four suicide attempts and more than 50 self-harm incidents in just five weeks in Banksia Hilll and Unit 18 combined.