Five young inmates stabbed as riot breaks out at Australian youth prison

Makeshift weapons have been used by inmates in an ongoing riot that has left at least six people injured at a juvenile justice centre on the NSW Central Coast.

The riot broke out at Frank Baxter Juvenile Justice Centre at Kariong about 10.30pm NZT yesterday, with reports several inmates assaulted each other, NSW Police said in a statement today.

Between 10 and 20 inmates are still "not where they should be" more than 12 hours after the riot started, Superintendent Tony Joice said.

Several inmates remain on the roof with some playing with tennis racquets and balls.

Four inmates have surrendered as police continue their negotiations alongside the riot squad, dog unit, PolAir helicopter and rescue unit.

"We have had some success," Supt Joice told reporters today. "We really encourage those that are left to think about their ongoing actions and to do likewise."

Police have established a secure perimeter inside the juvenile justice centre and restricted the armed detainees to a building within the complex.

The riot started when several inmates armed themselves with makeshift weapons and then assaulted other inmates within the centre, Supt Joice said.

"It seems a very sudden and unprovoked incident," he said. "Identifying the means and reasons why the assaults have taken place is part of the investigation."

An 18-year-old inmate has stab wounds and facial injuries and is in Royal North Shore Hospital in a serious condition.

Four others, aged between 17 and 20, also suffered stab wounds and have been taken to Gosford Hospital for treatment.

A 17-year-old youth has been taken to the same hospital after dislocating his ankle when he jumped off a roof.

Another inmate was treated at the scene for a broken nose.

All inmates have been accounted for, police said.