An inmate from a New South Wales central coast prison has died after falling 10 metres while trying to escape custody.

Corrective Services NSW said the 20-year-old man from the Kariong Correctional Centre was being transported from Gosford Hospital on Tuesday night when he broke free from two prison guards.

Corrective Services said the man jumped a 1.5-metre-high wall and fell down the 10-metre drop on the other side.

The prisoner was airlifted to Royal North Shore Hospital in a critical condition but was subsequently declared dead.

"Corrective Services NSW extends its sympathies to the family and friends," it said in a statement.

It said his death will be subject to a coronial inquest, as are all deaths in custody.

Prisoner Officers Vocational Branch chairperson Nicole Jess said she had spoken with the officers involved who were very distressed and were being supported.

"They've got to go through the investigations process and coroner's court, which will be very traumatic for them," Ms Jess said.

"The officers did attempt to stop him, one officer almost jumped over after him. It was very close, so it could have been two deaths. It's extremely tragic."

She said transporting patients was an extremely stressful process for prison guards.

"You are at your most vulnerable when you take a hospital escort out. You're dealing with the public and in a location that's unknown," Ms Jess said.

"You've got to be fully alert at all times."

She said they had been repeatedly calling on the Department of Corrections to help increase security and minimise risk in these hospital visits.

"We've asked the department to give us better equipment, to give us specific rooms in hospitals, to talk to hospitals about working with their security people, to do risk assessments of the hospitals," Ms Jess said.

"We believe there's better equipment that will help us.

"The department really needs to look at what's happening and give us the resources so we can manage the situation a lot better."