Police said the boy was using a trampoline placed under a clothes line in the backyard of his New Norfolk home, north west of Hobart, about 11.30am today.

As he jumped, the strap of his bicycle helmet got caught on the nylon rope of the clothes line and tightened around his neck.

The clothes line appeared to have swung away from the trampoline, leaving the boy suspended and unable to free himself, police said.

Attempts to resuscitate him were unsuccessful and he died at the scene.

Boy hangs himself in trampoline accident | National Breaking News | News.com.au