Teenager Alex Cross-Bennett knows his life could have taken a very different path if he did not have a foster carer — and he is one of the lucky ones, with a desperate shortage of carers for foster children his age in NSW.

Alex Cross-Bennett credits his foster family with turning his life around. ( ABC News )

"If I didn't have a foster carer … I'd probably be in jail," he said.

The Western Sydney teenager is studying to get his forklift licence, plans to join the Army and is dreaming of travelling.

He credits the family who took him in with turning his life around.

"I was a handful when I was 13 or 14, getting into trouble at school…but now I feel like I can accomplish anything if I try hard enough and push myself," he said.

Not-for-profit agencies are warning the lack of foster carers — especially for older children and teenagers — is reaching crisis level in some parts of Sydney.

Major increase in out-of-home care

Over the past decade, the number of children in out-of-home care in NSW has increased by almost 60 per cent from 11,843 to 18,659.

More than 11,000 of them are older children, between the ages of eight and 17.

Foster care manager from the not-for-profit Marist180 organisation, Hayley Clisby, said the situation in Western Sydney was particularly bad.

"They may be couch surfing and don't have a permanent place to call home," she said.

"In some cases we also have children and young people who are put in hotels and motels, which is really sad."

She said people from all walks of life could make great foster carers.

"Not everyone is suited to foster caring for a young child, but foster care for teens really opens the door to a variety of other people, including empty-nesters and singles," she said.

'Have you got rocks in your head?'

John Guthrie says it's great to see children become more confident over time. ( ABC News: Sarah Gerathy )

John Guthrie's friends thought he was crazy when he told them he and his partner Dennis Cash were going to foster teenagers.

"They always look at you and they think, teenage girls … have you got rocks in your head?"

Over the past 17 years they have fostered eight teenage girls through Barnardos.

He said teenagers often arrived frightened and reluctant to trust adults.

"It does take time and you notice the little things, you know it could just be a hug or an arm around your waist and you think 'oh OK, we've gotten somewhere, we've clicked'."

He said he had found foster caring very rewarding.

"You see that transition from a kid of 12 who has come in frightened … they blossom and they become these fabulous, self-assured young women and that's really good to see," he said.

Community Services Minister Pru Goward said the ice epidemic was partly to blame for the increase in children in out-of-home care, but hopes new early intervention programs could help bring the numbers down.

"If we could get on top of drug addiction in parents and the violence that comes with it then I think we could get that trajectory to change direction," she said.

However she pointed out that in the past 12 months NSW had seen a record number of out-of-home-care open adoptions — where foster carers adopt foster-placed children with the permission of their birth parents.

Finalised adoption orders have more than doubled to more than 127 cases compared to the previous year after the Government invested in additional case workers to speed up the adoption process.