Twenty-one people are facing charges after police stormed the roof of Frank Baxter Juvenile Justice Centre on Monday afternoon, bringing the incident to an end.

The riot broke out at the Kariong centre about 8.30pm on Sunday, with allegations several inmates assaulted each other, NSW Police said in a statement on Monday.

Seven were injured and six were taken to hospital, including an 18-year-old who was in a critical condition with stab wounds and facial injuries.

In a statement early on Tuesday, police said three men continued to receive treatment at Gosford Hospital.

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They included a man with stab wounds and a collapsed lung, another with head and face injuries and a third man with a broken ankle.

Police were in the process of charging 21 people with riot - five adults and 16 youths.

The adults were due to face the Gosford Local Court on Tuesday while the youths would appear in the Woy Woy Children's Court.

Families, Communities and Disability Services Minister Gareth Ward said the incident was unacceptable and the state government was treating it seriously.

Mr Ward said he has asked for an urgent independent review into the incident, to be conducted by former assistant police commissioner Lee Shearer.

"This inquiry will get to the bottom of what happened at Frank Baxter," Mr Ward said in a statement on Monday.

"While the incident will be subject to a police investigation, actions that put the safety and security of staff and detainees at risk will not be tolerated. Any detainees involved in instigating the incident will feel the full force of the law," Mr Ward said.

AAP