At about 11.30am the boy was jumping on a trampoline in his backyard.

Tasmania Police inspector Glen Woolley, of the Bridgewater Division, said the boy had placed the trampoline beneath a clothes line, to swing from the line.

The boy was wearing a bicycle helmet at the time and as he jumped between the nylon rope of the clothes line, the helmet strap became tangled and tightened around his neck.

It is believed the clothes line swung away from the trampoline, stranding the boy who was unable to free himself.

The boy's father found him a short time later and attempts to resuscitate him were unsuccessful. He died at the scene.

There are no suspicious circumstances.