At least 13 people currently serving jail time for high-level terrorism related convictions could be held indefinitely under legislation supported by federal and state attorneys-general in Canberra on Friday.

The Turnbull government is moving ahead with planned new national laws to allow the continued detention of jailed terrorists who still pose a risk after their prison terms expire.

The laws, criticised by some legal experts, could affect nine prisoners being held in NSW and four in Victoria, while a further 46 people facing charges or trial could also be affected, including 23 in NSW, 11 in Victoria and two in Queensland.

The plan, first announced in April, would see high-risk terrorists held in prison in the same way some convicted paedophiles and extreme violent offenders remain behind bars after their sentence under preventative measures.