Search continues for young escapees

The search is continuing for four juveniles who escaped custody by stealing a prison transport van at knife point while on an excursion in northern NSW.

The boys, three 18-year-olds and a 15-year-old, made a break for it while returning to a juvenile detention facility at Grafton on Sunday afternoon after a day excursion, police said.

Two of the boys threatened security guards with a knife and forced them from the van.

The guards weren't injured.

The boys sped off in the van and police were called to search for the group, who they believe could be heading to Casino.

Officers on Monday continued their hunt for Hakeem Cohen, Ezra Williams and Braiden Tighe, who are all described as appearing Aboriginal or Torres Strait Islander about 160 centimetres tall with medium builds and dark hair.

The 15-year-old, who can't be identified for legal reasons, is described as Caucasian, about 150cm tall with a thin build and brown hair.

Police say they shouldn't be approached and anyone who sees them should call 000.