A critically-endangered sea turtle has died at Auckland Zoo after ingesting enough plastic to fill a one litre container.

The female Hawksbill turtle washed up on the shores of Northland last month, weak and under-weight.

"We provided intensive care which included tube-feeding her to provide nutrition and we also gave her fluids, antibiotics and pain relief," Auckland Zoo resident vet Dr Lydia Uddstrom told 1 NEWS today.

"Despite her severe problems she initially improved and became a little stronger each day. However, after nearly two weeks of intensive care, her problems got the better of her, and she sadly died overnight."

A Massey University study recently suggested a third of turtles found dead on New Zealand beaches had ingested plastic, often mistaking plastic bags for jellyfish.

"Unfortunately, plastic inside the intestine looks the same on an x-ray as the turtle's intestines themselves. Sadly for this turtle, even if we had been able to detect the plastic earlier, she wasn't in a healthy enough state for us to surgically remove it," Uddstrom said.

Hawksbill turtles are found in tropical waters of the Atlantic, Pacific and Indian oceans.