More than half of the world's sea turtles are thought to have plastic in their guts as millions of tonnes of rubbish continues to be dumped into oceans each year, CSIRO researchers say.

An analysis of about 1000 turtles found dead on Australian beaches found hundreds of pieces of plastic in the animals' guts.

A turtle who has eaten one piece of plastic has a 22 per cent chance of dying, researchers say. Credit:Melbourne Zoo

These included plastic bags, hard plastic fragments, balloons, lolly wrappers and pieces of rope.

"Some of the turtles we studied had eaten only one piece of plastic, which was enough to kill it," Dr Kathy Townsend of the University of the Sunshine Coast said on Friday.